U.S. patent application number 11/214795 was filed with the patent office on 2006-01-12 for specification determining method, projection optical system making method and adjusting method, exposure apparatus and making method thereof, and computer system.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Masato Hamatani, Toshio Tsukakoshi.
Application Number | 20060007418 11/214795 |
Document ID | / |
Family ID | 27531805 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060007418 |
Kind Code |
A1 |
Hamatani; Masato ; et
al. |
January 12, 2006 |
Specification determining method, projection optical system making
method and adjusting method, exposure apparatus and making method
thereof, and computer system
Abstract
A computer system comprises a first computer into which target
information that an optical apparatus is to achieve is inputted and
a second computer that determines the specification of a projection
optical system based on the target information received from the
first computer via a communication path with using a wave-front
aberration amount, which the projection optical system is to
satisfy, as a standard. Therefore, in the process of making the
projection optical system, higher-order components of the
aberration as well as lower-order components can be simultaneously
corrected by adjusting the projection optical system based on the
result of measuring the wave-front aberration to satisfy the
specification, so that the making process becomes simpler.
Furthermore, the target that the exposure apparatus is to achieve
is securely achieved due to the projection optical system.
Inventors: |
Hamatani; Masato;
(Kounosu-shi, JP) ; Tsukakoshi; Toshio; (Anego
City, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
27531805 |
Appl. No.: |
11/214795 |
Filed: |
August 31, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10072866 |
Feb 12, 2002 |
6961115 |
|
|
11214795 |
Aug 31, 2005 |
|
|
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Current U.S.
Class: |
355/52 ;
355/55 |
Current CPC
Class: |
H01J 2237/30461
20130101; G03F 7/706 20130101; H01J 2237/30433 20130101 |
Class at
Publication: |
355/052 ;
355/055 |
International
Class: |
G03B 27/68 20060101
G03B027/68 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2001 |
JP |
2001-036182 |
Feb 13, 2001 |
JP |
2001-036184 |
Feb 26, 2001 |
JP |
2001-051178 |
Jan 31, 2002 |
JP |
2002-023547 |
Jan 31, 2002 |
JP |
2002-023567 |
Claims
1. A specification-determining method with which to determine a
specification of a projection optical system used in an optical
apparatus, said determining method comprising: obtaining target
information which said optical apparatus is to achieve; and
determining, based on said target information, the specification of
said projection optical system with using one of a wave-front
aberration amount and value corresponding to a wave-front
aberration, which said projection optical system is to satisfy, as
a standard.
2. A specification-determining method according to claim 1,
wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the coefficient of a specific term selected,
based on said target information, from coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded.
3. A specification-determining method according to claim 1,
wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value of coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded such that said RMS value within the entire field
of said projection optical system is not over a given limit.
4. A specification-determining method according to claim 1,
wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as standards the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded such that said coefficients are not over given
respective limits.
5. A specification-determining method according to claim 1,
wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value, within the field of said
projection optical system, of coefficients of n'th order, m.theta.
terms corresponding to a watched, specific aberration out of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded such that said RMS
value is not over a given limit.
6. A specification-determining method according to claim 1,
wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value, within the field of said
projection optical system, of coefficients of each group of
m.theta. terms having the same m.theta. value out of terms, which
correspond to a watched, specific aberration, out of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded such that said RMS value is not over a given
respective limit.
7. A specification-determining method according to claim 1,
wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value of coefficients given by
weighting according to said target information the coefficients of
terms of a Zernike polynomial in which a wave-front in said
projection optical system is expanded such that said RMS value of
the weighted coefficients is not over a given limit.
8. A specification-determining method according to claim 1, wherein
said target information includes information of a pattern subject
to projection by said projection optical system.
9. A specification-determining method according to claim 1, wherein
said optical apparatus is an exposure apparatus which transfers a
given pattern onto a substrate via said projection optical
system.
10. A specification-determining method according to claim 1,
wherein in the determining of said specification, based on
information of a pattern subject to projection by said projection
optical system, a simulation is performed that obtains a space
image formed on the image plane when said projection optical system
projects with said pattern, and wherein said simulation result is
analyzed to determine a limit for wave-front aberration as a
standard such that said pattern is transferred finely.
11. A specification-determining method according to claim 10,
wherein said simulation obtains said space image based on linear
combinations between sensitivities of coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded, to a specific aberration for said pattern as a
pattern subject to projection and the coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded, said sensitivities depending on said
pattern.
12. A projection-optical-system making method with which to make a
projection optical system used in an optical apparatus, said method
comprising: determining the specification of said projection
optical system according to the specification-determining method of
claim 1; and adjusting said projection optical system to satisfy
said specification.
13. A projection-optical-system making method according to claim
12, wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the coefficient of a specific term selected,
based on said target information, from coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded.
14. A projection-optical-system making method according to claim
12, wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value of coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded such that said RMS value within the entire field
of said projection optical system is not over a given limit.
15. A projection-optical-system making method according to claim
12, wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as standards the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded such that said coefficients are not over given
respective limits.
16. A projection-optical-system making method according to claim
12, wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value, within the field of said
projection optical system, of coefficients of n'th order, m.theta.
terms corresponding to a watched, specific aberration out of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded such that said RMS
value is not over a given limit.
17. A projection-optical-system making method according to claim
12, wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value, within the field of said
projection optical system, of coefficients of each group of
m.theta. terms having the same m.theta. value out of terms, which
correspond to a watched, specific aberration, out of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded such that said RMS value is not over a given
respective limit.
18. A projection-optical-system making method according to claim
12, wherein, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value of coefficients given by
weighting according to said target information the coefficients of
terms of a Zernike polynomial in which a wave-front in said
projection optical system is expanded such that said RMS value of
the weighted coefficients is not over a given limit.
19. A projection-optical-system making method according to claim
12, wherein in the determining of said specification a simulation
is performed that obtains a space image formed on the image plane
when said projection optical system projects with a pattern subject
to projection by said projection optical system, and wherein said
simulation result is analyzed to determine a limit for wave-front
aberration as a standard such that said pattern is transferred
finely.
20. A projection-optical-system making method according to claim
19, wherein said simulation obtains said space image based on
linear combinations between sensitivities of coefficients of terms
of a Zernike polynomial in which a wave-front in said projection
optical system is expanded, to a specific aberration for said
pattern as a pattern subject to projection and the coefficients of
terms of a Zernike polynomial in which a wave-front in said
projection optical system is expanded, said sensitivities depending
on said pattern.
21. A projection-optical-system making method according to claim
12, wherein said target information includes information of a
pattern subject to projection by said projection optical
system.
22. A projection-optical-system making method according to claim
12, wherein in adjusting said projection optical system, said
projection optical system is adjusted based on a result of
measuring a wave-front aberration in said projection optical system
so as to satisfy said specification.
23. A projection-optical-system making method according to claim
22, wherein said measuring of a wave-front aberration is performed
before installing said projection optical system in the main body
of said optical apparatus.
24. A projection-optical-system making method according to claim
22, wherein said measuring of a wave-front aberration is performed
after having installed said projection optical system in the main
body of said optical apparatus.
25. A projection-optical-system making method according to claim
12, wherein said optical apparatus is an exposure apparatus which
transfers a given pattern onto a substrate via said projection
optical system.
26. An exposure apparatus which transfers a pattern formed on a
mask onto a substrate via an exposure optical system, said exposure
apparatus comprising: a projection optical system made according to
the making method of claim 12 as said exposure optical system.
27. A device manufacturing method including a lithography process,
wherein in said lithography process, an exposure apparatus
according to claim 26 performs exposure.
28. A method with which to make an exposure apparatus, said method
comprising: making a projection optical system by using the
projection-optical-system making method of claim 12; and installing
said projection optical system in the exposure apparatus main
body.
29. A projection-optical-system making method with which to make a
projection optical system used in an exposure apparatus, said
method comprising: adjusting said projection optical system
according to exposure conditions scheduled to be used such that a
best focus position in at least one point of an exposure area
within the field of said projection optical system is displaced by
a given amount, said exposure area being illuminated with exposure
illumination light.
30. A projection-optical-system making method according to claim
29, wherein said exposure conditions include an illumination
condition that a coherence factor is smaller than 0.5.
31. A projection-optical-system making method according to claim
29, wherein said exposure conditions include use of
phase-shift-type masks.
32. An exposure apparatus which transfers a pattern formed on a
mask onto a substrate via an exposure optical system, said exposure
apparatus comprising: a projection optical system made according to
the making method of claim 29 as said exposure optical system.
33. A device manufacturing method including a lithography process,
wherein in said lithography process, an exposure apparatus
according to claim 32 performs exposure.
34. A method with which to make an exposure apparatus, said method
comprising: making a projection optical system by using the
projection-optical-system making method of claim 29; and installing
said projection optical system in the exposure apparatus main
body.
35. A projection-optical-system adjusting method with which to
adjust a projection optical system used in an exposure apparatus,
said adjusting method comprising: performing, when setting exposure
conditions that a phase-shift mask is used with a coherence factor
of smaller than 0.5 as an illumination condition, prior focus
correction that displaces a best focus position in at least one
point of an exposure area within the field of said projection
optical system by a given amount, said exposure area being
illuminated with exposure illumination light.
36. A projection-optical-system adjusting method according to claim
35, wherein said phase-shift mask is a space-frequency-modulation
type of phase-shift mask.
37. A projection-optical-system adjusting method according to claim
35, wherein said prior focus correction is implemented by adjusting
an aberration in said projection optical system.
38. An exposure apparatus which transfers a given pattern onto a
substrate via a projection optical system, said exposure apparatus
comprising: a wave-front measuring unit that measures a wave-front
in said projection optical system; an adjusting unit that adjusts a
state of an image of said pattern formed by said projection optical
system; and a controller that controls said adjusting unit using a
result of said wave-front measuring unit measuring a
wave-front.
39. An exposure apparatus according to claim 38, wherein said
adjusting unit comprises an imaging-characteristic adjusting
mechanism that adjusts the imaging-characteristic of said
projection optical system.
40. An exposure apparatus according to claim 39, wherein said
controller controls said imaging-characteristic adjusting mechanism
based on a space image of said pattern calculated based on linear
combinations between sensitivities, to a watched aberration, of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded and the coefficients
of terms of a Zernike polynomial in which a wave-front measured in
said projection optical system is expanded, such that said watched
aberration is not over a limit, said sensitivities depending on
said pattern.
41. A device manufacturing method including a lithography process,
wherein in said lithography process, an exposure apparatus
according to claim 38 performs exposure.
42. A computer system comprising: a first computer into which
target information that an optical apparatus is to achieve is
inputted; and a second computer which is connected to said first
computer via a communication path and determines the specification
of a projection optical system used in said optical apparatus based
on said target information received from said first computer via
said communication path with using one of a wave-front aberration
amount and value corresponding to a wave-front aberration, which
said projection optical system is to satisfy, as a standard.
43. A computer system according to claim 42, wherein said target
information includes information of a pattern subject to projection
by said projection optical system, and wherein said second computer
performs a simulation that obtains a space image formed on the
image plane when said projection optical system projects with said
pattern, based on said pattern information, and analyzes said
simulation result to determine a limit for wave-front aberration in
said projection optical system as a standard such that said pattern
is transferred finely.
44. A computer system according to claim 43, wherein said second
computer obtains said space image based on linear combinations
between sensitivities of coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded, to a specific aberration for said pattern as a pattern
subject to projection and the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded, said sensitivities depending on said pattern.
45. A computer system according to claim 42, wherein said optical
apparatus is an exposure apparatus which transfers a given pattern
onto a substrate via said projection optical system.
46. A computer system according to claim 42, wherein said
communication path is a local area network.
47. A computer system according to claim 42, wherein said
communication path includes a public telephone line.
48. A computer system according to claim 42, wherein said
communication path includes a radio line.
49. A computer system comprising: a first computer which is
connected to an exposure apparatus main body which transfers a
given pattern onto a substrate via a projection optical system; and
a second computer which is connected to said first computer via a
communication path, performs a simulation that obtains a space
image formed on the image plane when said projection optical system
projects with said pattern, based on information of said pattern
received from said first computer via said communication path and
known aberration information of said projection optical system, and
analyzes said simulation result to determine best exposure
conditions.
50. A computer system according to claim 49, wherein said pattern
information is part of exposure conditions that are inputted into
said first computer.
51. A computer system according to claim 49, further comprising: a
reading-in unit that reads in said pattern information recorded on
a mask on a path on which said mask is transported to said exposure
apparatus main body, wherein said pattern information is inputted
into said first computer via said reading-in unit.
52. A computer system according to claim 49, wherein said second
computer sends said best exposure conditions determined to said
first computer via said communication path.
53. A computer system according to claim 52, wherein said first
computer sets exposure conditions of said exposure apparatus main
body to said best exposure conditions.
54. A computer system according to claim 49, wherein said second
computer obtains said space image based on linear combinations
between sensitivities of coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded, to a specific aberration for said pattern as a pattern
subject to projection and the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded, which wave-front is obtained based on a result, sent
by said first computer via said communication path, of measuring a
wave-front in said projection optical system, said sensitivities
depending on said pattern.
55. A computer system according to claim 54, wherein said result of
measuring a wave-front is inputted into said first computer.
56. A computer system according to claim 54, further comprising: a
wave-front measuring unit that measures a wave-front in said
projection optical system, wherein said first computer itself
obtains said result of measuring a wave-front from said wave-front
measuring unit.
57. A computer system according to claim 49, wherein said best
exposure conditions include information of a pattern suitable for
exposure by said exposure apparatus main body.
58. A computer system according to claim 49, wherein said best
exposure conditions include at least one of an illumination
condition for transferring a given pattern and numerical aperture
of said projection optical system.
59. A computer system according to claim 49, wherein said best
exposure conditions include specification of aberration due to said
projection optical system upon transferring said given pattern.
60. A computer system according to claim 59, further comprising: an
imaging-characteristic adjusting mechanism that adjusts the
imaging-characteristic of said projection optical system provided
in said exposure apparatus main body connected to said second
computer via said communication path, wherein said second computer
controls said imaging-characteristic adjusting mechanism, based on
said best exposure conditions determined, to adjust the
imaging-characteristic of said projection optical system.
61. A computer system according to claim 49, wherein said
communication path is a local area network.
62. A computer system according to claim 49, wherein said
communication path includes a public telephone line.
63. A computer system according to claim 49, wherein said
communication path includes a radio line.
64. A computer system comprising: a first computer which is
connected to an exposure apparatus main body having a projection
optical system that projects an image of a given pattern onto a
substrate; an adjusting unit which adjusts a state of an image of
said pattern formed by said projection optical system; and a second
computer which is connected to said first computer via a
communication path, wherein said second computer calculates control
information with which to control said adjusting unit, using a
result of measuring a wave-front in said projection optical system,
which result has been received from said first computer via said
communication path, and wherein one of said first and second
computers controls said adjusting unit based on said control
information.
65. A computer system according to claim 64, wherein said result of
measuring a wave-front is inputted into said first computer.
66. A computer system according to claim 64, further comprising: a
wave-front measuring unit that measures a wave-front in said
projection optical system, wherein said first computer itself
obtains said result of measuring a wave-front from said wave-front
measuring unit.
67. A computer system according to claim 64, wherein said adjusting
unit comprises an imaging-characteristic adjusting mechanism that
adjusts the imaging-characteristic of said projection optical
system.
68. A computer system according to claim 67, wherein said first
computer sends information of said pattern used in said exposure
apparatus main body to said second computer via said communication
path, and wherein said second computer obtains a space image formed
on the image plane when said projection optical system projects
with said pattern by a simulation based on said pattern information
and said result of measuring a wave-front, calculates a limit for a
watched aberration due to said projection optical system at which
said space image is finely formed, and calculates control
information with which to control said imaging-characteristic
adjusting mechanism such that said watched aberration due to said
projection optical system is not over said limit.
69. A computer system according to claim 68, wherein said second
computer calculates a space image of said pattern based on linear
combinations between sensitivities, to a watched aberration, of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded and the coefficients
of terms of a Zernike polynomial in which a wave-front measured in
said projection optical system is expanded, said sensitivities
depending on said pattern.
70. A computer system according to claim 64, wherein a plurality of
sets of said exposure apparatus main body and said first computer
are provided, and said exposure apparatus main bodies each have
said adjusting unit, and wherein said second computer is connected
via said communication path to at least one of the set of said
plural first computers and the set of said plural adjusting
units.
71. A computer system according to claim 64, wherein said
communication path is a local area network.
72. A computer system according to claim 64, wherein said
communication path includes a public telephone line.
73. A computer system according to claim 64, wherein said
communication path includes a radio line.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a specification determining
method, a projection optical system making method and adjusting
method, an exposure apparatus and making method thereof, and a
computer system, and more specifically to a specification
determining method of determining the specification of a projection
optical system to be provided in an optical apparatus, a method of
making and a method of adjusting a projection optical system to be
provided in an optical apparatus, an exposure apparatus provided
with the projection optical system made according to the method of
a projection optical system and making method thereof, and a
computer system suitable for implementing the specification
determining method and adjusting the imaging characteristic of the
projection optical system provided in the exposure apparatus.
[0003] 2. Description of the Related Art
[0004] In a lithography process for manufacturing semiconductor
devices (CPU, DRAM, etc.), image picking-up devices (CCD, etc.),
liquid crystal display devices, membrane magnetic heads or the
like, exposure apparatuses have been used which form device
patterns on a substrate. Because of increasingly high integration
of semiconductor devices in these years, a step-and-repeat type of
reduction projection exposure apparatus (the so-called stepper)
that can form fine patterns on a substrate such as a wafer or glass
plate, a step-and-scan type of scan projection exposure apparatus
(the so-called scanning stepper) that is improved over the stepper,
or the like is mainly used.
[0005] In the process of manufacturing semiconductor devices,
because multiple layers each of which has a sub-circuit pattern
need to be overlaid and formed on a substrate, it is important to
accurately align a reticle (or mask) having a sub-circuit pattern
formed thereon with respect to the already-formed pattern in each
shot area on a substrate. In order to accurately align, the optical
characteristic of the projection optical system needs to be
precisely measured and adjusted to be in a desired state (for
example, a state where magnification error of the transferred image
of a reticle pattern relative to each shot area's pattern on the
substrate is corrected). It is remarked that, also when
transferring a reticle pattern for a first layer onto each shot
area of the substrate, the imaging characteristic of the projection
optical system is preferably adjusted in order to accurately
transfer reticle patterns for second and later layers onto each
shot area.
[0006] As the method of measuring the optical characteristic (the
imaging characteristic, etc.) of the projection optical system, a
method is mainly used which calculates the optical characteristic
based on the result of measuring a resist image obtained by
exposing a substrate through a measurement reticle having a
predetermined measurement pattern that remarkably responds to a
specific aberration, formed thereon and then developing the
substrate where the projected image of the measurement pattern is
formed, the method being called a "print method", hereinafter.
[0007] In exposure apparatuses of the prior art, measuring
lower-order aberrations such as Seidel's five aberrations, i.e.,
spherical aberration, coma, astigmatism, field curvature, and
distortion according to the print method and adjusting and managing
the above aberrations due to the projection optical system based on
the measuring result has been performed.
[0008] For example when measuring distortion due to the projection
optical system, a measurement reticle is used on which inner box
marks that each are a square having a dimension of 100 um and outer
box marks that each are a square having a dimension of 200 um are
formed, and after having transferred the inner or outer box marks
onto a wafer whose surface is coated with a resist through the
projection optical system, the wafer stage is moved and then the
other marks are transferred and overlaid onto the wafer through the
projection optical system. When the magnification is equal to 1/5
for example, the resist image of box-in-box marks appears, after
development of the wafer, in each of which a box mark having a
dimension of 20 um is located inside of a box mark having a
dimension of 40 um. And distortion due to the projection optical
system is detected by measuring the positional relation between
both the marks and deviation from their reference point in the
stage coordinate system.
[0009] Moreover, when measuring the coma, a measurement reticle is
used on which a line-and space pattern (hereinafter, referred to as
a "L/S") having five lines whose width is, for example, 0.9 um is
formed, and the pattern is transferred onto a wafer whose surface
is coated with a resist through the projection optical system. When
the magnification is equal to 1/5 for example, the resist image of
the L/S pattern appears, after development of the wafer, having a
line width of 0.18 um. And coma due to the projection optical
system is detected by measuring the widths L1, L5 of two lines in
both ends of the pattern and obtaining a line-width abnormal value
given by the following equation: the line-width abnormal
vale=(L1-L5)/(L1+L5) (1).
[0010] Moreover, in measuring a best focus position of the
projection optical system, a wafer is moved sequentially to a
plurality of positions along the optical axis direction which are a
given distance (step pitch) apart from each other, and the L/S
pattern is transferred each time onto a different area of the wafer
through the projection optical system. The wafer position
associated with one whose line width is maximal out of the resist
images of the L/S pattern, which appear after development of the
wafer, is adopted as the best focus position.
[0011] When measuring the spherical aberration, the measurement of
a best focus position is performed a plurality of times each time
with a different L/S pattern having a different duty ratio, and
based on the differences between the best focus positions, the
spherical aberration is obtained.
[0012] When measuring the field curvature, the measurement of a
best focus position is performed in a plurality of measurement
points within the field of the projection optical system, and based
on the measuring results, the field curvature is calculated using
the least-squares method.
[0013] In addition, when measuring the astigmatism due to the
projection optical system, the measurement of a best focus position
is performed with two kinds of periodic patterns whose period
directions are perpendicular to each other, and based on the
difference between the best focus positions, the astigmatism is
calculated.
[0014] In the prior art, the specification of a projection optical
system in the making of an exposure apparatus is determined
according to the same standard as in the above managing of the
optical characteristic of the projection optical system. That is,
the specification is determined such that the five aberrations
measured by the print method or obtained by a simulation
substantially equivalent thereto are at or below given respective
values.
[0015] However, because of the demand for further improved exposure
accuracy corresponding to increasingly high integration in these
years, measuring only the lower-order aberrations according to the
prior art method and, based on the measuring result, adjusting the
optical characteristic of the projection optical system does not
yield a desired result. The reason for that is as follows.
[0016] The space image of a measurement pattern, for example, a L/S
pattern has space-frequency components (intrinsic frequency
components), i.e. a fundamental wave corresponding to the L/S
period and higher harmonics, and the pattern determines the
space-frequencies of the components that pass through the pupil
plane of the projection optical system. Meanwhile, reticles having
various patterns are used in the actual manufacturing of devices,
the space images of which patterns include innumerable
space-frequency components. Therefore, the prior art method of
measuring and adjusting aberrations based on the limited
information hardly meet the demand for further improved exposure
accuracy.
[0017] In this case, although reticle patterns having intrinsic
frequency components that are missing in the information need to be
measured, it takes an enormous amount of measurement and time, so
that it is not practical.
[0018] Furthermore, because of the accuracy in measuring resist
images, which are affected by the intrinsic characteristic of the
resist, etc., the correlation between the resist image and a
corresponding optical image needs to be found before extracting
data from the measuring result.
[0019] Furthermore, when an aberration is large, the linearity of
the resist image to the corresponding space image of the pattern is
lost, so that accurate measurement of the aberration is difficult.
In this case, for the purpose of accurately measuring the
aberration, it is necessary to change the pattern-pitch, the line
width (space frequency), etc., of the measurement pattern of the
reticle, through trial and error, such that the intrinsic
characteristic of the resist can be measured (the linearity is
obtained).
[0020] For the same reason, the method of determining the
specification of a projection optical system according to the above
criteria has reached its limit. It is because a projection optical
system satisfying the specification determined obviously cannot
achieve exposure accuracy demanded at present and in the
future.
[0021] In such circumstances, the adjusting method has been adopted
where, when making a projection optical system according to the
specification determined, the positions, etc., of lens devices are
adjusted such that the Seidel's five aberrations (lower-order
aberrations) satisfy the determined specification, based on the
result of measuring the aberration due to the projection optical
system according to the print method after the assembly of the
projection optical system in the making process, and, after that,
detecting residual higher-order aberrations by a light-rays tracing
method and adjusting the positions, etc., of lens devices in the
projection optical system (additionally reprocessing such as
non-spherical-surface process, if necessary) are performed (refer
to Japanese Patent Laid-Open No. 10-154657).
[0022] However, the above method of making a projection optical
system needs the two steps of correcting lower-order aberrations
and correcting higher-order aberrations and also computation for
light-rays tracing that even super-computer will take several days
to perform.
[0023] Furthermore, when an aberration (non-linear aberration)
occurs by which the linearity of the resist image to the
corresponding space image of a pattern is lost, adjusting the
projection optical system in view of the order in which aberrations
are adjusted is needed. For example, when coma is large, the image
of a pattern is not resolved, so that accurate data of distortion,
astigmatism and spherical aberration cannot be obtained. Therefore,
it is necessary to measure coma using a pattern for accurate
measurement of coma and adjust the projection optical system to
make the coma small enough and then measure distortion, astigmatism
and spherical aberration and, based on the measuring result, adjust
the projection optical system. The fact that the order of measuring
the aberrations to be adjusted is specified means that the
selection of the lenses used is restricted.
[0024] In addition, the prior art method uses, regardless of what
maker the user of the exposure apparatus is, measurement patterns
suitable to measure the respective aberrations by in order to
determine the specification of the projection optical system and
adjust the optical characteristic, the measurement patterns
remarkably responding to the respective aberrations.
[0025] Meanwhile, the effects that the aberrations due to the
projection optical system have on the imaging characteristic for
various patterns are different. For example, contact-hole features
are more influenced by astigmatism than by the others while a fine
line-and-space pattern is more influenced by coma than by the
others. Furthermore, the best focus position is different between
an isolated line and line-and-space pattern.
[0026] Therefore, the optical characteristic (aberrations, etc.) of
the projection optical system and other capabilities of an exposure
apparatus actually differ between its users.
[0027] DISCLOSURE of INVENTION
[0028] This invention was made under such circumstances, and a
first purpose of the present invention is to provide a
specification determining method with which it is possible to
simplify the process of making a projection optical system
according to the determined specification and securely achieve a
target that an optical apparatus with the projection optical system
is to achieve.
[0029] Moreover, a second purpose of the present invention is to
provide a projection optical system making method with which it is
possible to simplify the process of making a projection optical
system and securely achieve a target that an optical apparatus is
to achieve.
[0030] A third purpose of the present invention is to provide an
adjusting method which can accurately and easily adjust the optical
characteristic of a projection optical system.
[0031] A fourth purpose of the present invention is to provide an
exposure apparatus which can accurately transfer a pattern on a
mask onto a substrate through the projection optical system and a
making method thereof.
[0032] Moreover, a fifth purpose of the present invention is to
provide a computer system with which it is possible to simplify the
process of making a projection optical system according to the
determined specification and securely achieve a target that an
optical apparatus with the projection optical system is to
achieve.
[0033] A sixth purpose of the present invention is to provide a
computer system which can automatically perform setting of desired
exposure conditions for an exposure apparatus.
[0034] According to a first aspect of the present invention, there
is provided a specification-determining method with which to
determine a specification of a projection optical system used in an
optical apparatus, said determining method comprising obtaining
target information which said optical apparatus is to achieve; and
determining, based on said target information, the specification of
said projection optical system with using one of a wave-front
aberration amount and value corresponding to a wave-front
aberration, which said projection optical system is to satisfy, as
a standard.
[0035] Herein, the value corresponding to a wave-front aberration
includes an index of the wave-front aberration such as a Zernike
coefficient, etc., and target information means a resolving power,
a minimum line width, the wavelength (center wavelength, wavelength
width, etc.) of illumination light incident on the projection
optical system, information of a pattern subject to projection,
other information about the projection optical system which
determines the capabilities of the optical apparatus, which
information can be a target for the projection optical system.
[0036] According to this method, the specification of a projection
optical system is determined based on target information which the
optical apparatus is to achieve, with using one of a wave-front
aberration amount and value corresponding to a wave-front
aberration, which the projection optical system is to satisfy, as a
standard. That is, the specification of the projection optical
system is determined using overall information as a standard, which
is information of the wave-front on the pupil plane of the
projection optical system and different from the above limited
information about light that passes through the pupil plane.
Therefore, in making the projection optical system according to the
determined specification, higher-order aberrations are
simultaneously corrected as well as lower-order aberrations by
adjusting the projection optical system based on the result of
measuring the wave-front aberration, so that the making process is
simplified. Furthermore, a target that an optical apparatus with
the projection optical system is to achieve can be securely
achieved.
[0037] In this case, there are various methods of determining the
specification of a projection optical system using a wave-front
aberration amount as a standard.
[0038] For example, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the coefficient of a specific term selected,
based on said target information, from coefficients of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded.
[0039] Alternatively, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value (Root-mean-square value) of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded such that said RMS
value within the entire field of said projection optical system is
not over a given limit.
[0040] Alternatively, in the determining of said specification, the
specification of said projection optical system is determined with
using as standards the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded such that said coefficients are not over given
respective limits.
[0041] Alternatively, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value, within the field of said
projection optical system, of coefficients of n'th order, m.theta.
terms corresponding to a watched, specific aberration out of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded such that said RMS
value is not over a given limit.
[0042] Alternatively, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value, within the field of said
projection optical system, of coefficients of each group of
m.theta. terms having the same m.theta. value out of terms, which
correspond to a watched, specific aberration, out of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded such that said RMS value is not over a given
respective limit.
[0043] Alternatively, in the determining of said specification, the
specification of said projection optical system is determined with
using as a standard the RMS value of coefficients given by
weighting according to said target information the coefficients of
terms of a Zernike polynomial in which a wave-front in said
projection optical system is expanded such that said RMS value of
the weighted coefficients is not over a given limit.
[0044] In the specification-determining method according to this
invention, said target information may include information of a
pattern subject to projection by said projection optical
system.
[0045] In the specification-determining method according to this
invention, said optical apparatus may be an exposure apparatus
which transfers a given pattern onto a substrate via said
projection optical system.
[0046] In the specification-determining method according to this
invention, in the determining of said specification, based on
information of a pattern subject to projection by said projection
optical system, a simulation may be performed that obtains a space
image formed on the image plane when said projection optical system
projects with said pattern, and said simulation result may be
analyzed to determine a limit for wave-front aberration as a
standard such that said pattern is transferred finely.
[0047] In this case, said simulation may obtain said space image
based on linear combinations between sensitivities (Zernike
Sensitivity) of coefficients of terms of a Zernike polynomial in
which a wave-front in said projection optical system is expanded,
to a specific aberration for said pattern as a pattern subject to
projection and the coefficients of terms of a Zernike polynomial in
which a wave-front in said projection optical system is expanded,
said sensitivities depending on said pattern. Here, "sensitivities
(Zernike Sensitivity) of coefficients of terms of a Zernike
polynomial" means the imaging capability of the projection optical
system under given exposure conditions, for example, variation per
1.lamda. in each of the coefficients of Zernike polynomial's terms
corresponding to various aberrations (or their indexes). Herein,
the term (Zernike Sensitivity) is used to denote such meaning.
[0048] According to a second aspect of the present invention, there
is provided a first projection-optical-system making method with
which to make a projection optical system used in an optical
apparatus, said method comprising determining the specification of
said projection optical system according to the
specification-determining method of this invention; and adjusting
said projection optical system to satisfy said specification.
[0049] According to this, the specification of a projection optical
system is determined by the specification-determining method based
on target information which the optical apparatus is to achieve,
with using a wave-front aberration amount, which the projection
optical system is to satisfy, as a standard. And the projection
optical system is adjusted to satisfy the specification. Therefore,
the projection optical system is adjusted to satisfy the
specification determined using overall information as a standard,
which is information of the wave-front on the pupil plane of the
projection optical system and different from the above limited
information about light that passes through the pupil plane. Here,
higher-order aberrations are adjusted as well as lower-order
aberrations, so that the two-step adjustment in the prior art and
light-rays tracing for adjustment of higher-order aberrations are
not necessary. Therefore, the process of making a projection
optical system is simplified. Furthermore, a target that an optical
apparatus with the projection optical system is to achieve can be
securely achieved.
[0050] In the first projection-optical-system making method
according to this invention, any of the various methods of
determining the specification of a projection optical system using
a wave-front aberration amount as a standard can be used. Moreover,
in the determining of said specification a simulation may be
performed that obtains a space image formed on the image plane when
said projection optical system projects with a pattern subject to
projection by said projection optical system, and said simulation
result may be analyzed to determine a limit for wave-front
aberration as a standard such that said pattern is transferred
finely. In this case, said simulation may obtain said space image
based on linear combinations between sensitivities of coefficients
of terms of a Zernike polynomial in which a wave-front in said
projection optical system is expanded, to a specific aberration for
said pattern as a pattern subject to projection and the
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded, said sensitivities
depending on said pattern.
[0051] In the first projection-optical-system making method
according to this invention, said target information may include
information of a pattern subject to projection by said projection
optical system.
[0052] In the first projection-optical-system making method
according to this invention, in adjusting said projection optical
system, said projection optical system may be adjusted based on a
result of measuring a wave-front aberration in said projection
optical system so as to satisfy said specification.
[0053] Here, "adjusting the projection optical system" means
changing the position (or distance from another), tilt, etc., of at
least one optical device of the projection optical system and, when
the optical device is a lens, changing its eccentricity or rotating
it about the optical axis, and replacing individually optical
devices of the projection optical system and, when the projection
optical system has a plurality of lens barrels, replacing lens
barrels as units, and, further, reprocessing at least one optical
device of the projection optical system, especially when the
optical device is a lens, processing its surface to become
non-spherical, if necessary. Herein, the expression "adjusting the
projection optical system" is used to denote such meaning.
[0054] In this case, said measuring of a wave-front aberration may
be performed before installing said projection optical system in
the main body of said optical apparatus, or said measuring of a
wave-front aberration may be performed after having installed said
projection optical system in the main body of said optical
apparatus.
[0055] In the first projection-optical-system making method
according to this invention, said optical apparatus may be an
exposure apparatus which transfers a given pattern onto a substrate
via said projection optical system.
[0056] According to a third aspect of the present invention, there
is provided a second projection-optical-system making method with
which to make a projection optical system used in an exposure
apparatus, said method comprising adjusting said projection optical
system according to exposure conditions scheduled to be used such
that a best focus position in at least one point of an exposure
area within the field of said projection optical system is
displaced by a given amount, said exposure area being illuminated
with exposure illumination light.
[0057] According to this, corresponding to exposure conditions
scheduled to be used, the projection optical system is adjusted
such that the best focus position in at least one point of an
exposure area within the field of the projection optical system is
displaced by a given amount, the exposure area being illuminated
with exposure illumination light. That is, under certain exposure
conditions, the best focus position within the exposure area may
deviate due to the aberrations of the projection optical system
(e.g. astigmatism, spherical aberration, etc.), so that the depth
of focus becomes smaller. According to this invention, the
projection optical system is made in which the best focus position
in at least one point of an exposure area is corrected according to
exposure conditions. Therefore, an exposure apparatus having the
projection optical system installed therein can perform exposure
under the exposure conditions, where the deviation of the best
focus position is greatly reduced and the depth of focus is larger
than before.
[0058] In this case, said exposure conditions may include an
illumination condition that a coherence factor is smaller than
0.5.
[0059] In the second projection-optical-system making method
according to this invention, said exposure conditions may include
use of phase-shift-type masks.
[0060] According to a fourth aspect of the present invention, there
is provided a first exposure apparatus which transfers a pattern
formed on a mask onto a substrate via an exposure optical system,
said exposure apparatus comprising a projection optical system made
according to one of the first and second making methods of this
invention as said exposure optical system.
[0061] According to this, when the first exposure apparatus
comprises a projection optical system made according to the first
making method as the exposure optical system, because in the
projection optical system higher-order aberrations have been
adjusted as well as lower-order aberrations, it can accurately
transfer the pattern of a mask onto a substrate. When the first
exposure apparatus comprises a projection optical system made
according to the second making method as the exposure optical
system, it can perform exposure under the exposure conditions,
where the deviation of the best focus position is greatly reduced
and the depth of focus is larger than before. Therefore, the first
exposure apparatus can perform exposure with high accuracy.
[0062] According to a fifth aspect of the present invention, there
is provided a method with which to make an exposure apparatus, said
method comprising making a projection optical system by using one
of the first and second making methods of this invention; and
installing said projection optical system in the exposure apparatus
main body.
[0063] According to a sixth aspect of the present invention, there
is provided a first projection-optical-system adjusting method with
which to adjust a projection optical system used in an optical
apparatus, said adjusting method comprising measuring a wave-front
in said projection optical system; and adjusting said projection
optical system based on a result of said measuring of a
wave-front.
[0064] According to this, the projection optical system is adjusted
based on the result of measuring the wave-front in the projection
optical system. Therefore, the projection optical system is
adjusted based on the result of measuring overall information which
is information of the wave-front on the pupil plane of the
projection optical system and different from the above limited
information about light that passes through the pupil plane. Here,
higher-order aberrations are adjusted as well as lower-order
aberrations with no need to consider the order of aberrations like
in the prior art. Therefore, the optical characteristic of the
projection optical system can be very accurately and easily
adjusted.
[0065] In this case, in said adjusting, said projection optical
system may be adjusted such that the coefficient of a specific term
selected, based on target information, from coefficients of terms
of a Zernike polynomial in which a wave-front in said projection
optical system is expanded is not over a given limit.
[0066] Alternatively, in said adjusting, said projection optical
system is adjusted such that the RMS value of coefficients of terms
of a Zernike polynomial in which said wave-front within the entire
field of said projection optical system is expanded is not over a
given limit.
[0067] Alternatively, in said adjusting, said projection optical
system is adjusted such that the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded are not over given respective limits.
[0068] Alternatively, in said adjusting, said projection optical
system is adjusted such that the RMS value, within the field of
said projection optical system, of coefficients of n'th order,
m.theta. terms corresponding to a watched, specific aberration out
of coefficients of terms of a Zernike polynomial in which a
wave-front in said projection optical system is expanded is not
over a given limit.
[0069] Alternatively, in said adjusting, said projection optical
system is adjusted such that the RMS value, within the field of
said projection optical system, of coefficients of each group of
m.theta. terms having the same m.theta. value out of terms, which
correspond to a watched, specific aberration, out of terms of a
Zernike polynomial in which a wave-front in said projection optical
system is expanded is not over a given respective limit.
[0070] When the first projection-optical-system adjusting method
according to this invention further comprises obtaining information
of a pattern subject to projection in said projection optical
system, said projection optical system, in said adjusting, may be
adjusted based on a space image of said pattern calculated based on
linear combinations between sensitivities (Zernike Sensitivity), to
a watched aberration, of coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded and the coefficients of terms of a Zernike polynomial
in which a wave-front measured in said projection optical system is
expanded, such that said watched aberration is not over a limit,
said sensitivities depending on said pattern.
[0071] When the first projection-optical-system adjusting method
according to this invention further comprises obtaining target
information that said optical apparatus is to achieve, said
projection optical system, in said adjusting, may be adjusted such
that the RMS value of coefficients given by weighting according to
said target information the coefficients of terms of a Zernike
polynomial in which a wave-front in said projection optical system
is expanded is not over a given limit.
[0072] In this case, said target information may include
information of a pattern subject to projection by said projection
optical system.
[0073] In the first projection-optical-system adjusting method
according to this invention, various methods may be used to measure
the wave-front; for example, in measuring said wave-front, a
wave-front in said projection optical system may be measured based
on a result of printing a given pattern on a wafer via a pinhole
and said projection optical system, or a wave-front in said
projection optical system may be measured based on a space image
formed via a pinhole and said projection optical system.
[0074] According to a seventh aspect of the present invention,
there is provided a second projection-optical-system adjusting
method with which to adjust a projection optical system used in an
exposure apparatus, said adjusting method comprising performing,
when setting exposure conditions that a phase-shift mask is used
with a coherence factor of smaller than 0.5 as an illumination
condition, prior focus correction that displaces a best focus
position in at least one point of an exposure area within the field
of said projection optical system by a given amount, said exposure
area being illuminated with exposure illumination light.
[0075] According to this, when setting exposure conditions that a
phase-shift mask is used with a coherence factor of smaller than
0.5 as an illumination condition, prior focus correction is
performed that displaces a best focus position in at least one
point of an exposure area within the field of the projection
optical system by a given amount, the exposure area being
illuminated with exposure illumination light. Therefore, the
projection optical system can perform exposure under the exposure
conditions, where the deviation of the best focus position is
greatly reduced and the depth of focus is larger than before.
[0076] In this case, although the phase-shift mask may be of a
half-tone type or of another type, said phase-shift mask is
preferably a space-frequency-modulation type of phase-shift
mask.
[0077] In the second projection-optical-system adjusting method
according to this invention, said prior focus correction may be
implemented by adjusting an aberration in said projection optical
system.
[0078] According to an eighth aspect of the present invention,
there is provided a second exposure apparatus which transfers a
given pattern onto a substrate via a projection optical system,
said exposure apparatus comprising a wave-front measuring unit that
measures a wave-front in said projection optical system; an
adjusting unit that adjusts a state of an image of said pattern
formed by said projection optical system; and a controller that
controls said adjusting unit using a result of said wave-front
measuring unit measuring a wave-front.
[0079] According to this, a wave-front measuring unit measures a
wave-front in the projection optical system, and a controller
controls an adjusting unit using the result of measuring the
wave-front that provides overall information about light passing
through the pupil plane of the projection optical system.
Therefore, because the state of the image of the pattern formed by
the projection optical system is automatically adjusted based on
the result of measuring the wave-front, the projection optical
system can accurately transfer the pattern onto a substrate.
[0080] In this case, the construction of the adjusting unit does
not matter as long as it can adjust the state of the image of the
pattern formed by the projection optical system. For example, said
adjusting unit may comprise an imaging-characteristic adjusting
mechanism that adjusts the imaging-characteristic of said
projection optical system.
[0081] In the second exposure apparatus according to this
invention, said controller may control said imaging-characteristic
adjusting mechanism based on a space image of said pattern
calculated based on linear combinations between sensitivities
(Zernike Sensitivity), to a watched aberration, of coefficients of
terms of a Zernike polynomial in which a wave-front in said
projection optical system is expanded and the coefficients of terms
of a Zernike polynomial in which a wave-front measured in said
projection optical system is expanded, such that said watched
aberration is not over a limit, said sensitivities depending on
said pattern.
[0082] According to a ninth aspect of the present invention, there
is provided a first computer system comprising a first computer
into which target information that an optical apparatus is to
achieve is inputted; and a second computer which is connected to
said first computer via a communication path and determines the
specification of a projection optical system used in said optical
apparatus based on said target information received from said first
computer via said communication path with using one of a wave-front
aberration amount and value corresponding to a wave-front
aberration, which said projection optical system is to satisfy, as
a standard.
[0083] According to this, target information that an optical
apparatus is to achieve is inputted into a first computer, and a
second computer determines the specification of a projection
optical system based on the target information received from the
first computer via the communication path with using one of a
wave-front aberration amount and value corresponding to a
wave-front aberration, which the projection optical system is to
satisfy, as a standard. That is, the specification of the
projection optical system is determined using overall information
as a standard, which is information of the wave-front on the pupil
plane of the projection optical system and different from the above
limited information about light that passes through the pupil
plane. Therefore, in making the projection optical system according
to the determined specification, higher-order aberrations are
simultaneously corrected as well as lower-order aberrations by
adjusting the projection optical system based on the result of
measuring the wave-front aberration, so that the making process is
simplified. Furthermore, a target that an optical apparatus with
the projection optical system is to achieve can be securely
achieved.
[0084] In this case, when said target information includes
information of a pattern subject to projection by said projection
optical system, said second computer may perform a simulation that
obtains a space image formed on the image plane when said
projection optical system projects with said pattern, based on said
pattern information, and analyze said simulation result to
determine a limit for wave-front aberration in said projection
optical system as a standard such that said pattern is transferred
finely.
[0085] In this case, said second computer may obtain said space
image based on linear combinations between sensitivities of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded, to a specific
aberration for said pattern as a pattern subject to projection and
the coefficients of terms of a Zernike polynomial in which a
wave-front in said projection optical system is expanded, said
sensitivities depending on said pattern.
[0086] In the first computer system according to this invention,
said optical apparatus may be, among various apparatuses, an
exposure apparatus which transfers a given pattern onto a substrate
via said projection optical system.
[0087] According to a tenth aspect of the present invention, there
is provided a second computer system comprising a first computer
which is connected to an exposure apparatus main body which
transfers a given pattern onto a substrate via a projection optical
system; and a second computer which is connected to said first
computer via a communication path, performs a simulation that
obtains a space image formed on the image plane when said
projection optical system projects with said pattern, based on
information of said pattern received from said first computer via
said communication path and known aberration information of said
projection optical system, and analyzes said simulation result to
determine best exposure conditions.
[0088] According to this, a second computer performs a simulation
that obtains a space image formed on the image plane when the
projection optical system projects with the pattern, based on
information of the pattern received from the first computer via the
communication path and known aberration information of the
projection optical system, and analyzes the simulation result to
determine best exposure conditions. Therefore, optimum exposure
conditions can be set almost automatically.
[0089] In this case, said pattern information may be part of
exposure conditions that are inputted into said first computer, or,
when the computer system further comprises a reading-in unit that
reads in said pattern information recorded on a mask on a path on
which said mask is transported to said exposure apparatus main
body, said pattern information may be inputted into said first
computer via said reading-in unit.
[0090] In the second computer system according to this invention,
said second computer may send said best exposure conditions
determined to said first computer via said communication path.
[0091] In this case, said first computer may set exposure
conditions of said exposure apparatus main body to said best
exposure conditions.
[0092] In the second computer system according to this invention,
said second computer may obtain said space image based on linear
combinations between sensitivities (Zernike Sensitivity) of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded, to a specific
aberration for said pattern as a pattern subject to projection and
the coefficients of terms of a Zernike polynomial in which a
wave-front in said projection optical system is expanded, which
wave-front is obtained based on a result, sent by said first
computer via said communication path, of measuring a wave-front in
said projection optical system, said sensitivities depending on
said pattern.
[0093] In this case, said result of measuring a wave-front may be
inputted into said first computer, or, when the computer system
further comprises a wave-front measuring unit that measures a
wave-front in said projection optical system, said first computer
itself may obtain said result of measuring a wave-front from said
wave-front measuring unit.
[0094] In the second computer system according to this invention,
said best exposure conditions may include, among various things,
information of a pattern suitable for exposure by said exposure
apparatus main body, or said best exposure conditions may include
at least one of an illumination condition for transferring a given
pattern and numerical aperture of said projection optical
system.
[0095] Further, said best exposure conditions may include
specification of aberration due to said projection optical system
upon transferring said given pattern. In this case, when the
computer system further comprises an imaging-characteristic
adjusting mechanism that adjusts the imaging-characteristic of said
projection optical system provided in said exposure apparatus main
body connected to said second computer via said communication path,
said second computer may control said imaging-characteristic
adjusting mechanism, based on said best exposure conditions
determined, to adjust the imaging-characteristic of said projection
optical system.
[0096] According to an eleventh aspect of the present invention,
there is provided a third computer system comprising a first
computer which is connected to an exposure apparatus main body
having a projection optical system that projects an image of a
given pattern onto a substrate; an adjusting unit which adjusts a
state of an image of said pattern formed by said projection optical
system; and a second computer which is connected to said first
computer via a communication path, wherein said second computer
calculates control information with which to control said adjusting
unit, using a result of measuring a wave-front in said projection
optical system, which result has been received from said first
computer via said communication path, and wherein one of said first
and second computers controls said adjusting unit based on said
control information.
[0097] According to this, a first computer sends the result of
measuring a wave-front in the projection optical system to a second
computer through a communication path. And the second computer
calculates control information with which to control the adjusting
unit, using a result of measuring a wave-front in the projection
optical system, which result has been received from the first
computer via the communication path, and one of the first and
second computers controls the adjusting unit based on the control
information. Therefore, the state of an image of said pattern
formed by said projection optical system is accurately adjusted
using the information of the wave-front on the pupil plane of the
projection optical system, that is, overall information about light
passing through the pupil plane. In this case, the second computer
can be placed remote from the exposure apparatus main body and the
first computer connected thereto, in which case the remote system
calculates control information with which to control the adjusting
unit, and the state of the image of the pattern formed by the
projection optical system can be very accurately adjusted based on
the control information.
[0098] In the third computer system according to this invention,
said result of measuring a wave-front is inputted into said first
computer, or, when the computer system further comprises a
wave-front measuring unit that measures a wave-front in said
projection optical system, said first computer itself may obtain
said result of measuring a wave-front from said wave-front
measuring unit. In the latter case, the first computer connected to
the exposure apparatus main body measures a wave-front in said
projection optical system by using a wave-front measuring unit in a
so-called self-measuring manner, and the state of an image of said
pattern formed by said projection optical system is almost
automatically and accurately adjusted.
[0099] In the third computer system according to this invention,
the construction of the adjusting unit does not matter as long as
it can adjust the state of the image of the pattern formed by the
projection optical system. For example, said adjusting unit may
comprise an imaging-characteristic adjusting mechanism that adjusts
the imaging-characteristic of said projection optical system.
[0100] In this case, said first computer may send information of
said pattern used in said exposure apparatus main body to said
second computer via said communication path, and said second
computer may obtain a space image formed on the image plane when
said projection optical system projects with said pattern by a
simulation based on said pattern information and said result of
measuring a wave-front, calculates a limit for a watched aberration
due to said projection optical system at which said space image is
finely formed, and calculate control information with which to
control said imaging-characteristic adjusting mechanism such that
said watched aberration due to said projection optical system is
not over said limit.
[0101] In this case, said second computer may calculate a space
image of said pattern based on linear combinations between
sensitivities (Zernike Sensitivity), to a watched aberration, of
coefficients of terms of a Zernike polynomial in which a wave-front
in said projection optical system is expanded and the coefficients
of terms of a Zernike polynomial in which a wave-front measured in
said projection optical system is expanded, said sensitivities
depending on said pattern.
[0102] In the third computer system according to this invention,
only one exposure apparatus main body and only one first computer
connected thereto may be provided, or, when a plurality of sets of
said exposure apparatus main body and said first computer are
provided, and said exposure apparatus main bodies each have said
adjusting unit, said second computer may be connected via said
communication path to at least one of the set of said plural first
computers and the set of said plural adjusting units.
[0103] In the first, second, and third computer systems according
to this invention, various things can be used as the communication
path. That is, said communication path may be a local area network,
or said communication path may include a public telephone line, or
said communication path may include a radio line.
[0104] In addition, in a lithography process, by one of the first
and second exposure apparatuses according to this invention
performing exposure, patterns can be accurately formed on a
substrate, and highly integrated micro-devices can be manufactured
with high yield. Therefore, according to another aspect of the
present invention, there is provided a device manufacturing method
using one of the first and second exposure apparatuses (i.e., a
device manufacturing method comprising the step of transferring a
pattern onto a photosensitive object by using one of the first and
second exposure apparatuses).
BRIEF DESCRIPTION OF THE DRAWINGS
[0105] In the accompanying drawings:
[0106] FIG. 1 is a schematic view showing the construction of a
computer system according to an embodiment of this invention;
[0107] FIG. 2 is a schematic view showing the construction of a
first exposure apparatus 122.sub.1 in FIG. 1;
[0108] FIG. 3 is a cross-sectional view of an exemplary
wave-front-aberration measuring unit;
[0109] FIG. 4A is a view showing light beams emitted from
micro-lens array when there is no aberration in the optical
system;
[0110] FIG. 4B is a view showing light beams emitted from
micro-lens array when there is aberration in the optical
system;
[0111] FIG. 5 is a flow chart showing a process algorithm executed
by a CPU in the second communication server when setting best
exposure conditions of an exposure apparatus;
[0112] FIG. 6 is a schematic, oblique view of a measurement
reticle;
[0113] FIG. 7 is a schematic view showing an X-Z cross-section,
near the optical axis AX, of the measurement reticle mounted on a
reticle stage along with a projection optical system;
[0114] FIG. 8 is a schematic view showing an X-Z cross-section of
the -Y direction end of the measurement reticle mounted on a
reticle stage along with the projection optical system;
[0115] FIG. 9A is a view showing a measurement pattern formed on
the measurement reticle of this embodiment;
[0116] FIG. 9B is a view showing a reference pattern formed on the
measurement reticle of this embodiment;
[0117] FIG. 10A is a view showing one of reduced images (latent
images) of the measurement pattern formed a given distance apart
from each other on the resist layer on a wafer;
[0118] FIG. 10B is a view showing the positional relation between
the latent image in FIG. 10A of the measurement pattern and the
latent image of the reference pattern;
[0119] FIG. 11 is a flow chart schematically showing the process of
making the projection optical system; and
[0120] FIG. 12 is a schematic view showing the construction of a
computer system modified.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0121] An embodiment of the present invention will be described
below based on FIGS. 1 to 11.
[0122] FIG. 1 shows the schematic construction of a computer system
according to an embodiment of this invention.
[0123] A computer system 10 shown in FIG. 1 comprises a lithography
system 112 in a semiconductors-manufacturing factory of a device
maker (hereinafter, called "maker A" as needed), which is a user of
a device manufacturing apparatus such as an exposure apparatus, and
a computer system 114 of an exposure apparatus maker (hereinafter,
called "maker B" as needed) connected via a communication line
including the public telephone line 116 to part of the lithography
system 112.
[0124] The lithography system 112 comprises a communication server
120 as a first computer, a first, second and third exposure
apparatuses 122.sub.1, 122.sub.2, 122.sub.3 as optical apparatuses,
and a first proxy server 124 for verification, all of which are
connected with each other via a local area network (LAN) 118.
[0125] The communication server 120 and a first through third
exposure apparatuses 122.sub.1, 122.sub.2, 122.sub.3 are assigned
addresses AD1 through AD4 with which to distinguish them
respectively.
[0126] The first proxy server 124 is provided between the LAN 118
and the public telephone line 116 and serves as a kind of firewall.
That is, the first proxy server 124 prevents communication data
flowing through the LAN 118 from leaking to the outside, allows
only information from the outside having one of the addresses AD1
through AD4 to pass through it and blocks the passage of other
information, so that the LAN 118 is protected against unjust
invasion from the outside.
[0127] The computer system 114 comprises a second proxy server 128
for verification, a second communication server 130 as a second
computer and the like, all of which are connected with each other
via a local area network (LAN) 126. The second communication server
130 is assigned an address AD5 with which to identify it.
[0128] The second proxy server 128, in the same way as the first
proxy server 124, prevents communication data flowing through the
LAN 126 from leaking to the outside and serves as a kind of
firewall that protects the LAN 126 against unjust invasion from the
outside.
[0129] In this embodiment, data from the first through third
exposure apparatuses 122.sub.1, 122.sub.2, 122.sub.3 is transferred
to the outside via the first communication server 120 and the first
proxy server 124, and data to the first through third exposure
apparatuses 122.sub.1, 122.sub.2, 122.sub.3 is transferred from the
outside via the first proxy server 124 or via the first proxy
server 124 and the first communication server 120.
[0130] FIG. 2 shows the schematic construction of the first
exposure apparatus 122.sub.1, which is a reduction projection
exposure apparatus of a step-and-repeat type, i.e. a stepper, using
a pulse-laser light source as an exposure light source
(hereinafter, called a "light source").
[0131] The exposure apparatus 122.sub.1 comprises an illumination
system composed of a light source 16 and illumination optical
system 12, a reticle stage RST as a mask stage holding a reticle R
as a mask illuminated with exposure illumination light EL as an
energy beam from the illumination system, a projection optical
system PL as an exposure optical system, which projects exposure
illumination light EL from the reticle R onto a wafer W as a
substrate which is on the image plane, a wafer stage WST on which a
Z-tilt stage 58 for holding the wafer W is mounted, and a control
system for controlling these.
[0132] The light source 16 is a pulse-ultraviolet light source that
emits pulse light having a wavelength in the vacuum-ultraviolet
range such as F.sub.2 laser (a wavelength of 157 nm) or ArF laser
(a wavelength of 193 nm). Alternatively the light source 16 may be
a light source that emits pulse light having a wavelength in the
far-ultraviolet or ultraviolet range such as KrF excimer laser (a
wavelength of 248 nm).
[0133] The light source 16 is disposed, in practice, in a service
room having low cleanliness that is separate from a clean room
where a chamber 11 housing an exposure-apparatus main body composed
of various elements of the illumination optical system 12, the
reticle stage RST, the projection optical system PL, the wafer
stage WST, etc., is disposed, and is connected to the chamber 11
via a light-transmitting optical system (not shown) including at
least part of an optical-axis adjusting optical system called a
beam-matching unit. The light source 16 is controlled by an
internal controller thereof according to control-information TS
from a main controller 50 in terms of switching the output of laser
beam LB, the energy of laser beam LB per pulse, output-frequency
(pulse frequency), the center wavelength and half band width in
spectrum (width of the wavelength range) and the like.
[0134] The illumination optical system 12 comprises a cylinder
lens, a beam expander (none are shown), a beam-shaping,
illuminance-uniformalizing optical system 20 having an optical
integrator (homogenizer) 22 therein, an illumination-system
aperture stop plate 24, a first relay lens 28A, a second relay lens
28B, a reticle blind 30, a mirror M for deflecting the optical
path, and a condenser lens 32. The optical integrator is a fly-eye
lens, a rod-integrator (inner-side-reflective-type integrator) or a
diffracting optical device. In this embodiment a fly-eye lens is
used as the optical integrator 22, which is also referred to as a
fly-eye lens 22.
[0135] The beam-shaping, illuminance-uniformalizing optical system
20 is connected through a light transmission window 17 provided on
the chamber 11 to the light-transmitting optical system (not
shown), and gets the cross section of laser beam LB, which is
incident thereon through the light transmission window 17 from the
light source 16, to be shaped by the cylinder lens or beam
expander, for example. The fly-eye lens 22 in the exit side of the
beam-shaping, illuminance-uniformalizing optical system 20 forms,
from the laser beam having its cross-section shaped, a surface
illuminant (secondary illuminant) composed of a lot of point
illuminants (illuminant images) on the focal plane on the output
side, which plane substantially coincides with the pupil plane of
the illumination optical system 12 in order to illuminate the
reticle R with uniform illuminace. The laser beam emitted from the
secondary illuminant is called "illumination light EL"
hereinafter.
[0136] The illumination-system aperture stop plate 24 constituted
by a disk-like member is disposed near the focal plane on the exit
side of the fly-eye lens 22. And arranged at almost regular pitches
along a circle on the illumination-system aperture stop plate 24
are, e.g., a usual aperture stop (usual stop) constituted by a
circular opening, a aperture stop (small-.sigma. stop) for making
coherence factor .sigma. small which is constituted by a small,
circular opening, a ring-like aperture stop (ring stop) for forming
a ring of illumination light, and a deformation aperture stop for a
deformation illuminant method composed of a plurality of openings
arranged eccentrically, of which two types of aperture stops are
shown in FIG. 1. The illumination-system aperture stop plate 24 is
constructed and arranged to be rotated by a driving unit 40 such as
a motor controlled by the main controller 50, and one of the
aperture stops is selectively set to be on the optical path of the
illumination light EL, so that the shape of the illuminant surface
in Koehler illumination described later is a ring, a small circle,
a large circle, four eyes or the like.
[0137] Instead of the aperture stop plate 24 or in combination with
it, for example, a plurality of diffracting optical devices
disposed in the illumination optical system, a movable prism
(conical prism, polyhedron prism, etc.) along the optical axis of
the illumination optical system, and an optical unit comprising at
least one zoom optical system are preferably arranged between the
light source 16 and the optical integrator 22, and by making
variable, when the optical integrator 22 is a fly-eye lens, the
intensity distribution of the illumination light on the incidence
surface thereof or, when the optical integrator 22 is an
inner-face-reflective-type integrator, the range of incidence angle
of the illumination light to the incidence surface, light-amount
distribution (the size and shape of the secondary illuminant) of
the illumination light on the pupil plane of the illumination
optical system is preferably adjusted, that is, loss of light due
to the change of conditions for illuminating the reticle R is
preferably suppressed. It is noted that in this embodiment a
plurality of illuminant images (virtual images) formed by the
inner-face-reflective-type integrator are also referred to as a
secondary illuminant.
[0138] Disposed on the optical path of the illumination light EL
from the illumination-system aperture stop plate 24 is a relay
optical system composed of the first and second relay lenses 28A,
28B, between which the reticle blind 30 is disposed. The reticle
blind 30, in which a rectangular opening for defining a rectangular
illumination area IAR on the reticle R is made, is disposed on a
plane conjugate to the pattern surface of the reticle R, and is a
blind whose opening is variable in shape and set by the main
controller 50 based on blind-setting information also called
masking information.
[0139] Disposed on the optical path of the illumination light EL
behind the second relay lens 28B forming part of the relay optical
system is the deflecting mirror M for reflecting the illumination
light EL having passed through the second relay lens 28B toward the
reticle R, and on the optical path of the illumination light EL
behind the mirror M, the condenser lens 32 is disposed.
[0140] In the construction described above, the incidence surface
of the fly-eye lens 22, the plane on which the reticle blind 30 is
disposed, and the pattern surface of the reticle R are optically
conjugate to each other, while the illuminant surface formed on the
focal plane on the exit side of the fly-eye lens 22 (the pupil
plane of the illumination optical system) and the Fourier transform
plane of the projection optical system PL (the exit pupil plane)
are optically conjugate to each other, and these form a Koehler
illumination system.
[0141] The operation of the illumination optical system having the
above construction will be described briefly in the following. The
laser beam LB emitted in pulse out of the light source 16 is made
incident on the beam-shaping, illuminance-uniformalizing optical
system 20 which shapes the cross section thereof, and then is made
incident on the fly-eye lens 22. By this, the secondary illuminant
is formed on the focal plane on the exit side of the fly-eye lens
22.
[0142] The illumination light EL emitted out of the secondary
illuminant passes through an aperture stop on the
illumination-system aperture stop plate 24, the first relay lens
28A, the rectangular aperture of the reticle blind 30, and the
second relay lens 28B in that order and then is deflected
vertically and toward below by the mirror M and, after passing
through the condenser lens 32, illuminates the rectangular
illumination area IAR on the reticle R held on the reticle stage
RST.
[0143] A reticle R is loaded onto the reticle stage RST and is held
by electrostatic chuck, vacuum chuck or the like (not shown). The
reticle stage RST is constructed to be able to be finely driven
(including rotation) on a horizontal plane (an X-Y plane) by a
driving system (not shown). It is remarked that the position of the
reticle stage RST is measured by a position detector such as a
reticle laser interferometer with given resolving power of, e.g.,
0.5 to 1 nm to supply the measurement results to the main
controller 50.
[0144] It is noted that the material for the reticle R depends on
the light source used. That is, when ArF excimer laser or KrF
excimer laser is used as the light source, synthetic quartz,
fluoride crystal such as fluorite, fluorine-doped quartz or the
like can be used while, when F.sub.2 laser is used as the light
source, fluoride crystal such as fluorite, fluorine-doped quartz or
the like needs to be used.
[0145] The projection optical system PL is, for example, a
reduction system that is telecentric bilaterally, and the
projection magnification of the projection optical system PL is,
e.g., 1/4, 1/5 or 1/6. Therefore, when the illumination area IAR on
the reticle R is illuminated with the illumination light EL as is
described above, the image of the pattern on the reticle R is
reduced to the projection magnification times the original size and
projected and transferred by the projection optical system PL onto
a rectangular area IA on a wafer W coated with a resist
(photosensitive material), which area IA usually coincides with a
shot area.
[0146] The projection optical system PL is a refractive system
composed of a plurality of refracting optical devices 13 (lens
devices), e.g. about 10 to 20 ones, as shown in FIG. 2. A plurality
of lens devices 13.sub.1, 13.sub.2, 13.sub.3, 13.sub.4 (considering
four ones for the sake of brief description) in the object-plane
side (reticle R side) of the projection optical system PL out of
the plurality of lens devices 13 are movable lenses that can be
driven by an imaging-characteristic correcting controller 48. The
lens devices 13.sub.1, through 13.sub.4 are held in a lens-barrel
via double-structured lens holders (not shown) respectively. The
lens devices 13.sub.1, 13.sub.2, 13.sub.4 of these are held by
inner lens holders each of which is supported at three points
against a respective outer lens holder by driving devices such as
piezo devices (not shown). By independently adjusting the voltages
applied to the driving devices, the lens devices 13.sub.1,
13.sub.2, 13.sub.4 can be shifted in a Z-direction, the optical
axis direction of the projection optical system PL and tilted
relative to the X-Y plane, that is, rotated about the X- and
Y-axes. The lens device 13.sub.3 is held by an inner lens holder
(not shown), and between the outer-circle side face of the inner
lens holder and the inner-circle side face of the outer lens
holder, driving devices such as piezo devices are disposed at
almost regular pitches each of which covers an angle of, e.g., 90
degrees. And adjusting the voltages applied to two opposite driving
devices the lens device 13.sub.3 can be shifted two-dimensionally
in the X-Y plane.
[0147] The other lens devices 13 are held in the lens-barrel via a
usual lens holder. It is noted that not being limited to the lens
devices 13.sub.1 through 13.sub.4, lenses near the pupil plane, or
in the image plane side, of the projection optical system PL or an
aberration-correcting plate (optical plate) for correcting the
projection optical system PL in terms of aberration, especially
clockwise asymmetric component thereof, may be constructed to be
able to be driven. Furthermore, the degree of freedom of those
optical devices (the number of directions in which to be movable)
may be one or more than three, not being limited to two or
three.
[0148] Moreover, near the pupil plane of the projection optical
system PL, an aperture stop 15 whose numerical aperture (N.A.) is
variable continuously in a predetermined range is disposed, is a
so-called iris aperture stop, for example, and is controlled by the
main controller 50.
[0149] It is noted that the material for the lens devices of the
projection optical system PL is fluoride crystal such as fluorite,
fluorine-doped quartz, synthetic quartz, or the like when ArF
excimer laser or KrF excimer laser is used as the illumination
light EL or, when F.sub.2 laser is used, fluoride crystal such as
fluorite or fluorine-doped quartz.
[0150] The wafer stage WST is constructed to be driven freely on
the X-Y two-dimensional plane by a wafer-stage driving portion 56
including a linear motor, and on a Z-tilt stage 58 mounted on the
wafer stage WST, a wafer W is held via a wafer holder (not shown)
by electrostatic chuck, vacuum chuck or the like.
[0151] Furthermore, the Z-tilt stage 58 is constructed to be able
to be positioned in the X-Y plane on the wafer stage WST and to be
tilted relative to the X-Y plane as well as to be movable in the
Z-direction so that the surface of a wafer W held on the Z-tilt
stage 58 can be set at a specified position (position in the
Z-direction and tilt to the X-Y plane).
[0152] Moreover, fixed on the Z-tilt stage 58 is a movable mirror
52W, through which a wafer laser interferometer 54W externally
disposed measures the position in the X- and Y-directions and
.theta..sub.Z direction (counterclockwise about the Z-axis) of the
Z-tilt stage 58, and position information measured by the wafer
laser interferometer 54W is supplied to the main controller 50,
which controls the wafer stage WST (and the Z-tilt stage 58) based
on the position information via the wafer-stage driving portion 56
including the driving systems of the wafer stage WST and the Z-tilt
stage 58.
[0153] A reference mark plate FM having reference marks including
one for base-line measurement is disposed on the Z-tilt stage 58
such that the surface thereof substantially coincides in height
with the surface of the wafer W.
[0154] A wave-front-aberration measuring unit 80 that is attachable
and detachable and portable is disposed on the side face in the +X
direction of the Z-tilt stage 58 (right side of the drawing of FIG.
2).
[0155] The wave-front-aberration measuring unit 80, as shown in
FIG. 3, comprises a housing 82, a light-receiving optical system 84
composed of a plurality of optical devices arranged in a
predetermined positional relation in the housing 82, and a
light-receiving portion 86 arranged in the end in the +Y direction
of the housing 82.
[0156] The cross section along the Y-Z plane of the housing 82
having a space therein is shaped like an "L", and in the topside
(in the +Z direction) thereof, an opening 82a which is circular in
a plan view is made so that light from above the housing 82 can be
made incident through it. Furthermore, a cover glass 88 is provided
so as to cover the opening 82a from inside the housing 82. Formed
on the upper surface of the cover glass 88 by deposition of metal
such as chrome is a shielding membrane having a circular opening in
the center thereof, which stops unnecessary light from entering the
light-receiving optical system 84 in measuring wave-front
aberration due to the projection optical system PL.
[0157] The light-receiving optical system 84 comprises an objective
lens 84a, a relay lens 84b, and a deflecting mirror 84c, which are
arranged in that order from under the cover glass 88 in the housing
82, and a collimator lens 84d and a micro-lens array 84e, which are
arranged in that order on the +Y side of the deflecting mirror 84c.
The deflecting mirror 84c is fixed to make an angle of 45 degrees
with the Z- and Y-directions so that light incident vertically from
above on the objective lens 84a is deflected toward the collimator
lens 84d. It is noted that the optical elements of the
light-receiving optical system 84 are fixed on the inner wall of
the housing 82 via holding members (not shown). The micro-lens
array 84e has a plurality of small convex lenses (lens devices)
arranged in an array on a plane perpendicular to the optical
path.
[0158] The light-receiving portion 86 comprises a light-receiving
device such as two-dimensional CCD and an electric circuit such as
a charge-transfer controlling circuit. The light-receiving device
has a size enough to receive all rays of light sent from the
micro-lens array 84e after having passed through the objective lens
84a. Data measured by the light-receiving portion 86 is sent to the
main controller 50 via a signal line (not shown) or by radio.
[0159] The wave-front-aberration measuring unit 80 can measure the
wave-front aberration due to the projection optical system PL while
the projection optical system PL is fixed in the exposure-apparatus
main body. The method of measuring the wave-front aberration due to
the projection optical system PL by using the wave-front-aberration
measuring unit 80 will be described later.
[0160] Referring back to FIG. 2, the exposure apparatus 122.sub.1
further comprises an oblique incidence type of multi-focus-position
detection system composed of a light source switched by the main
controller 50, an illumination system 60a for sending out imaging
beams, which form a lot of pinhole or slit images, toward the image
plane of the projection optical system PL and in an oblique
direction to the optical axis AX, and a light-receiving system 60b
for receiving the imaging beams reflected by the surface of the
wafer W, the multi-focus-position detection system being simply
called a "focus detection system" hereinafter. The focus detection
system (60a, 60b) has the same construction as is disclosed in, for
example, Japanese Patent Laid-Open No. 6-283403 and U.S. Pat. No.
5,448,332 corresponding thereto. The disclosure in the above U.S.
Patent is incorporated herein by reference as long as the national
laws in designated states or elected states, to which this
international application is applied, permit.
[0161] The main controller 50, upon exposure and the like, controls
the Z-position and the tilt relative to the X-Y plane of the wafer
W via the wafer-stage driving portion 56 based on the focus
deviation signal (defocus signal) such as an S-curve signal from
the light-receiving system 60b such that the focus deviation
becomes zero, by which auto-focus and auto-leveling are performed.
Furthermore, the main controller 50 measures the Z-position of the
wave-front-aberration measuring unit 80 and positions it by using
the focus detection system (60a, 60b) when measuring the wave-front
aberration as described later. Here, the tilt of the
wave-front-aberration measuring unit 80 may also be measured, if
necessary.
[0162] The exposure apparatus 122.sub.1 further comprises an
alignment system ALG of an off-axis type for measuring the
positions of, e.g., alignment marks on a wafer W held on the wafer
stage WST and the reference mark formed on the reference mark plate
FM. The alignment system ALG is an FIA (Field Image Alignment)
sensor of an image-processing type which directs, e.g., a detection
beam whose frequency band is broad for resist on the wafer not to
sense to a target mark and which picks up images of the target mark
formed on the receiving plane by the beam reflected from the target
mark and an index (not shown), by a pick-up device (CCD, etc.) with
outputting the pick-up signals thereof. Not being limited to the
FIA system, an alignment sensor which directs a coherent detection
beam to a target mark and detects the beam scattered or diffracted
from the target mark or an alignment sensor which detects the
interference of two order sub-beams (e.g., of the same order)
diffracted from the target mark or the combination of the two may
be used, needless to say.
[0163] Moreover, above the reticle R in the exposure apparatus
122.sub.1 of this embodiment, a pair of reticle alignment
microscopes (not shown) each constituted by a TTR (Through The
Reticle) alignment optical system for simultaneously observing a
reticle mark on the reticle R and a corresponding reference mark on
the reference mark plate through the projection optical system PL
using light having the same wavelength as exposure light are
provided. The reticle alignment microscope has the same
construction as is disclosed in, for example, Japanese Patent
Laid-Open No. 7-176468 and U.S. Pat. No. 5,646,413 corresponding
thereto. The disclosure in the above U.S. Patent is incorporated
herein by reference as long as the national laws in designated
states or elected states, to which this international application
is applied, permit.
[0164] The control system includes the main controller 50 in FIG. 2
which is constituted by a work station (or microcomputer)
comprising a CPU (Central Processing Unit) ROM (Read Only Memory),
RAM (Random Access Memory), etc., and which controls the entire
apparatus overall as well as the above operations. The main
controller 50 controls between-shots stepping of the wafer stage,
exposure timing and the like overall.
[0165] Furthermore, for example, a storage unit 42 constituted by
hard disks, an input unit 45 comprising a pointing-device such as
the mouse, a display unit 44 such as a CR.sub.T display or
liquid-crystal display, and a drive unit for information-recording
media such as CD-ROM, DVD-ROM, MO, FD, etc., are externally
connected to the main controller 50. And the main controller 50 is
connected with the LAN 118.
[0166] An information-recording medium provided in the drive unit
46 (hereinafter, CD-ROM for the sake of convenience) stores a
conversion program (hereinafter, called a "first program" for the
sake of convenience) for converting position deviations measured by
the wave-front-aberration measuring unit 80 as described later into
coefficients of the Zernike polynomial.
[0167] The second and third exposure apparatuses 122.sub.2,
122.sub.3 have the same construction as the exposure apparatus
122.sub.1.
[0168] Next, the method of measuring wave-front-aberration in the
exposure apparatus 122.sub.1 through 122.sub.3 upon maintenance,
etc., will be described assuming for the sake of simplicity that
the wave-front-aberration due to the light-receiving optical system
84 of the wave-front-aberration measuring unit 80 is
negligible.
[0169] As a premise, it is supposed that the first program of the
CD-ROM in the driving unit 46 has been installed in the storage
unit 42.
[0170] Upon usual exposure operation, because the
wave-front-aberration measuring unit 80 is detached from the Z-tilt
stage 58, a service engineer, operator or the like (hereinafter,
called "service engineer, etc.," as needed) first attaches the
wave-front-aberration measuring unit 80 to the side face of the
Z-tilt stage 58. Here, the wave-front-aberration measuring unit 80
is fixed on a predetermined reference surface (herein, the side
face in the +X direction) by bolts, magnets or the like, so that
the wave-front-aberration measuring unit 80 can be put in place
within the stroke distance of the wafer stage WST (the Z-tilt stage
58) when measuring the wave-front-aberration.
[0171] After the completion of the attaching, the main controller
50, according to a measurement-start command inputted by the
service engineer, etc., moves the wafer stage WST via the
wafer-stage driving portion 56 such that the wave-front-aberration
measuring unit 80 is put underneath the alignment system ALG,
detects an alignment mark (not shown) provided on the
wave-front-aberration measuring unit 80 by the alignment system
ALG, and, based on the detection result and values measured at the
same time by the laser interferometer 54W, calculates the position
coordinates of the alignment mark to obtain the accurate position
of the wave-front-aberration measuring unit 80. And after the
measuring of the wave-front-aberration measuring unit 80's
position, the main controller 50 measures the wave-front-aberration
in the manner described below.
[0172] The main controller 50 loads a measurement reticle, on which
pinhole features are formed, (not shown; called a "pinhole reticle"
hereinafter) onto the reticle stage RST by a reticle loader (not
shown). The pinhole reticle is one on the pattern surface of which
pinholes are formed in a plurality of points within an area
identical to the illumination area IAR, each of the pinholes being
an ideal point illuminant and producing a spherical wave.
[0173] It is noted that a diffusion plate, for example, is provided
on the upper surface of the pinhole reticle so that the wave front
of the beam passing through the projection optical system PL and
the wave-front-aberration can be measured for all N.A.'s of the
projection optical system PL.
[0174] After loading the pinhole reticle, the main controller 50
detects the reticle alignment mark of the pinhole reticle by the
reticle alignment microscopes and, based on the detection result,
positions the pinhole reticle in a predetermined position, so that
the center of the pinhole reticle almost coincides with the optical
axis of the projection optical system PL.
[0175] After that, the main controller 50 gives control information
TS to the light source 16 to make it generate laser beam LB. By
this, the pinhole reticle is illuminated with the illumination
light EL from the illumination optical system 12. Then light from
each of the plurality of pinholes of the pinhole reticle is focused
through the projection optical system PL on the image plane to form
a pinhole image.
[0176] Next, the main controller 50 moves the wafer stage WST via
the wafer-stage driving portion 56, while monitoring measurement
values of the laser interferometer 54W, such that the center of the
opening 82a of the wave-front-aberration measuring unit 80 almost
coincides with the imaging point where an image of a given pinhole
on the pinhole reticle is formed. At the same time, the main
controller 50 finely moves the Z-tilt stage 58 in the Z-direction
via the wafer-stage driving portion 56 based on the detection
result of the focus detection system (60a, 60b) such that the upper
surface of cover glass 88 of the wave-front-aberration measuring
unit 80 coincides with the image plane on which the pinhole images
are formed, as well as adjusting the tilt angle of the wafer stage
WST as needed. By this, the light beam from the given pinhole are
made incident through the center opening of the cover glass 88 on
the light-receiving optical system 84 and received by the
light-receiving device of the light-receiving portion 86.
[0177] The operation will be described in more detail below. A
spherical wave is produced from the given pinhole on the pinhole
reticle. The spherical wave is made incident on the projection
optical system PL and passes through the light-receiving optical
system 84 of the wave-front-aberration measuring unit 80, i.e., the
objective lens 84a, the relay lens 84b, the mirror 84c and the
collimator lens 84d which produces parallel rays of the light that
illuminate the micro-lens array 84e. By this, the pupil plane of
the projection optical system PL is relayed to and divided by the
micro-lens array 84e. Each lens device of the micro-lens array 84e
focuses respective light on the receiving surface of the
light-receiving device to form a pinhole image on the receiving
surface.
[0178] If the projection optical system PL is an ideal optical
system that does not cause the wave-front-aberration, the
wave-front takes an ideal shape (herein, a flat plane) on the pupil
plane of the projection optical system PL, and thus the parallel
rays of the light incident on the micro-lens array 84e come to form
a plane wave with an ideal wave-front, in which case a respective
spot-image (hereinafter, also called a "spot") is, as shown in FIG.
4A, formed on the optical axis of each lens device of the
micro-lens array 84e.
[0179] However, because the projection optical system PL usually
causes wave-front-aberration, the wave-front formed by the parallel
rays of the light incident on the micro-lens array 84e deviates
from the ideal wave-front, and according to the deviation, that is,
the tilt angle of the wave-front to the ideal wave-front, the
imaging point of each spot deviates from the optical axis of a
respective lens device forming part of the micro-lens array 84e as
shown in FIG. 4B. Here, the deviation of each spot from the
respective reference point corresponds to the tilt angle of the
wave-front.
[0180] And the light-receiving device forming part of the
light-receiving portion 86 converts light (beam for the spot image)
incident and focused on each focus point thereon into an electric
signal, which is sent to the main controller 50 via an electric
circuit. The main controller 50 calculates the imaging position of
each spot based on the electric signal and then a position
deviation (.DELTA..xi., .DELTA..eta.) based on the calculation
result and known position data of the respective reference point
and stores the position deviation (.DELTA..xi., .DELTA..eta.) in
the RAM, during which the main controller 50 receives a
corresponding measurement value (X.sub.i, Y.sub.i) from the laser
interferometer 54W.
[0181] After the wave-front-aberration measuring unit 80 has
measured the position deviations of the spot images for the imaging
point of the given pinhole, the main controller 50 moves the wafer
stage WST such that the center of the opening 82a of the
wave-front-aberration measuring unit 80 almost coincides with the
imaging point of a next pinhole. After that, in the same way as
described above, the main controller 50 makes the light source 16
generate laser beam LB and calculates the imaging position of each
spot. For the imaging points of the other pinholes the same
measurement sequence is repeated. It is remarked that in the above
measurement, the position, size, etc., of the illumination area on
the reticle may be changed for each given pinhole by using the
reticle blind 30 such that only the given pinhole or some pinholes
including the given pinhole are illuminated with the illumination
light EL.
[0182] After the completion of all the necessary measurements, the
RAM of the main controller 50 stores the position deviations
(.DELTA..xi., .DELTA..eta.) of the spot images for the imaging
point of each pinhole and the coordinate data of the imaging point
(the corresponding measurement value (X.sub.i, Y.sub.i) measured by
the laser interferometer 54W upon measurement for the imaging point
of the pinhole).
[0183] Next, the main controller 50 loads the first program into
the main memory and computes, according to the principle described
below, the wave-front (wave-front aberration) for the imaging
points of the pinholes, i.e. the first through n'th measurement
points within the field of the projection optical system PL,
specifically, the coefficients of the Zernike polynomial given by
an equation (4) shown below, e.g. the second term's coefficient
Z.sub.2 through the 37th term's coefficient Z.sub.37, based on the
position deviations (.DELTA..xi., .DELTA..eta.) of the spot images
for the imaging point of each pinhole and the coordinate data of
the imaging point in the RAM by using the first program.
[0184] In this embodiment, the wave-front of light having passed
through the projection optical system PL is obtained based on the
position deviations (.DELTA..xi., .DELTA..eta.) by using the first
program. The position deviations (.DELTA..xi., .DELTA..eta.)
directly reflect the tilts of the wave-front to the ideal
wave-front to the degree that the wave-front is drawn based on the
position deviations (.DELTA..xi., .DELTA..eta.). It is remarked
that, as is obvious from the physical relationship between the
position deviations (.DELTA..xi., .DELTA..eta.) and the wave-front,
the principle in this embodiment for calculating the wave-front is
the known Shack-Hartmann principle.
[0185] Next, the method of calculating the wave-front based on the
above position deviations will be described briefly.
[0186] As described above, integrating the position deviations
(.DELTA..xi., 66 .eta.), which correspond to the tilts of the
wave-front, gives the shape of the wave-front (strictly speaking,
deviations from a reference plane (the ideal plane)). Let W(x, y)
indicate the wave-front (deviations from the reference plane) and k
be a proportional coefficient, then the following equations (2),
(3) exist. .DELTA. .times. .times. .xi. = k .times. .times.
.differential. W .differential. x ( 2 ) .DELTA. .times. .times.
.eta. = k .times. .times. .differential. W .differential. y ( 3 )
##EQU1##
[0187] Because it is not appropriate to directly integrate the
tilts of the wave-front obtained only in the spot positions, the
shape of the wave-front is fitted by and expanded in a series whose
terms are orthogonal. The Zernike polynomial is a series suitable
to expand a surface symmetrical around an axis in, where its
component tangent to a circle is expanded in a trigonometric
series. That is, the wave-front W is expanded in the equation (4)
when using a polar coordinate system (.rho., .theta.). W .function.
( .rho. , .theta. ) = i .times. Z i f i .function. ( .rho. ,
.theta. ) ( 4 ) ##EQU2##
[0188] Because the terms are orthogonal, coefficients Z.sub.i of
the terms can be determined independently. The "i" may terminate at
a certain number with an effect of a sort of filtering. The first
through 37th terms (Z.sub.i.times.f.sub.i) are shown in Table 1 as
examples. Although the 37th term in Table 1 is, in practice, the
49th term of the Zernike polynomial, in this embodiment it is
treated as the 37th term. That is, in this embodiment there is no
limit to the number of the terms of the Zernike polynomial.
TABLE-US-00001 TABLE 1 Z.sub.i f.sub.i Z.sub.1 1 Z.sub.2 .rho. cos
.theta. Z.sub.3 .rho. sin .theta. Z.sub.4 2.rho..sup.2 - 1 Z.sub.5
.rho..sup.2 cos 2.theta. Z.sub.6 .rho..sup.2 sin 2.theta. Z.sub.7
(3.rho..sup.3 - 2.rho.) cos .theta. Z.sub.8 (3.rho..sup.3 - 2.rho.)
sin .theta. Z.sub.9 6.rho..sup.4 - 6.rho..sup.2 + 1 Z.sub.10
.rho..sup.3 cos 3.theta. Z.sub.11 .rho..sup.3 sin 3.theta. Z.sub.12
(4.rho..sup.4 - 3.rho..sup.2) cos 2.theta. Z.sub.13 (4.rho..sup.4 -
3.rho..sup.2) sin 2.theta. Z.sub.14 (10.rho..sup.5 - 12.rho..sup.3
+ 3.rho.) cos .theta. Z.sub.15 (10.rho..sup.5 - 12.rho..sup.3 +
3.rho.) sin .theta. Z.sub.16 20.rho..sup.6 - 30.rho..sup.4 +
12.rho..sup.2 - 1 Z.sub.17 .rho..sup.4 cos 4.theta. Z.sub.18
.rho..sup.4 sin 4.theta. Z.sub.19 (5.rho..sup.5 - 4.rho..sup.3) cos
3.theta. Z.sub.20 (5.rho..sup.5 - 4.rho..sup.3) sin 3.theta.
Z.sub.21 (15.rho..sup.6 - 20.rho..sup.4 + 6.rho..sup.2) cos
2.theta. Z.sub.22 (15.rho..sup.6 - 20.rho..sup.4 + 6.rho..sup.2)
sin 2.theta. Z.sub.23 (35.rho..sup.7 - 60.rho..sup.5 +
30.rho..sup.3 - 4.rho.) cos .theta. Z.sub.24 (35.rho..sup.7 -
60.rho..sup.5 + 30.rho..sup.3 - 4.rho.) sin .theta. Z.sub.25
70.rho..sup.8 - 140.rho..sup.6 + 90.rho..sup.4 - 20.rho..sup.2 + 1
Z.sub.26 .rho..sup.5 cos 5.theta. Z.sub.27 .rho..sup.5 sin 5.theta.
Z.sub.28 (6.rho..sup.6 - 5.rho..sup.4) cos 4.theta. Z.sub.29
(6.rho..sup.6 - 5.rho..sup.4) sin 4.theta. Z.sub.30 (21.rho..sup.7
- 30.rho..sup.5 + 10.rho..sup.3) cos 3.theta. Z.sub.31
(21.rho..sup.7 - 30.rho..sup.5 + 10.rho..sup.3) sin 3.theta.
Z.sub.32 (56.rho..sup.8 - 105.rho..sup.6 + 60.rho..sup.4 -
10.rho..sup.2) cos 2.theta. Z.sub.33 (56.rho..sup.8 -
105.rho..sup.6 + 60.rho..sup.4 - 10.rho..sup.2) sin 2.theta.
Z.sub.34 (126.rho..sup.9 - 280.rho..sup.7 + 210.rho..sup.5 -
60.rho..sup.3 + 5.rho.) cos .theta. Z.sub.35 (126.rho..sup.9 -
280.rho..sup.7 + 210.rho..sup.5 - 60.rho..sup.3 + 5.rho.) sin
.theta. Z.sub.36 252.rho..sup.10 - 630.rho..sup.8 + 560.rho..sup.6
- 210.rho..sup.4 + 30.rho..sup.2 - 1 Z.sub.37 924.rho..sup.12 -
2772.rho..sup.10 + 3150.rho..sup.8 - 1680.rho..sup.6 +
420.rho..sup.4 - 42.rho..sup.2 + 1
[0189] Because the position deviations detected are the
differentials of the wave front, fitting the differential
coefficients for the terms to the position deviations is performed
in practice. When expressed in a polar coordinate system
(x=.rho.cos .theta., y=.rho.sin .theta.), the equations (5), (6)
exist. .differential. W .differential. x = .differential. W
.differential. .rho. .times. .times. cos .times. .times. .theta. -
1 .rho. .times. .times. .differential. W .differential. .theta.
.times. .times. sin .times. .times. .theta. ( 5 ) .differential. W
.differential. y = .differential. W .differential. .rho. .times.
.times. sin .times. .times. .theta. + 1 .rho. .times. .times.
.differential. W .differential. .theta. .times. .times. cos .times.
.times. .theta. ( 6 ) ##EQU3##
[0190] Because the differentials of the terms of the Zernike
polynomial are not orthogonal, the least-squares method is used in
the fitting. Because the information (position deviation) of each
spot image is expressed in two coordinates X and Y, let n indicate
the number of the pinholes (e.g. n=about 81 to 400), then the
number of sets of equations given by the equations (2) through (6)
is 2n (=about 162 to 800).
[0191] Each term of the Zernike polynomial corresponds to an
optical aberration. Lower-order terms (i's value being small)
almost correspond to Seidel's aberrations. Therefore, the
wave-front aberration due to the projection optical system PL can
be expressed by the Zernike polynomial.
[0192] The computation procedure of the first program is determined
according to the above principle, and executing the first program
gives the wave-front information (wave-front aberration) for the
first through n'th measurement points within the field of the
projection optical system PL, specifically, the coefficients of
terms of the Zernike polynomial, e.g. the second term's coefficient
Z.sub.2 through the 37th term's coefficient Z.sub.37.
[0193] In the description below, the wave-front data (wave-front
aberration) for the first through n'th measurement points within
the field of the projection optical system PL is expressed by
column matrix Q given by the equation (7). Q = [ P 1 P 2 P n ] ( 7
) ##EQU4##
[0194] In the equation (7), each of the elements P.sub.1 through
P.sub.n of matrix Q indicates a column matrix (vector) made up of
the second through the 37th terms' coefficients (Z.sub.2 to
Z.sub.37) of the Zernike polynomial.
[0195] The main controller 50 stores the wave-front data (e.g. the
second term's coefficient Z.sub.2 through the 37th term's
coefficient Z.sub.37 of the Zernike polynomial) obtained in the
above manner in the storage unit 42.
[0196] Moreover, the main controller 50, according to an inquiry
from the first communication server 120, reads out the wave-front
data from the storage unit 42 and sends it to the first
communication server 120 via LAN 118.
[0197] Referring back to FIG. 1, stored in the hard disk or the
like of the first communication server 120 are information about
targets to be achieved in the first through third exposure
apparatuses 122.sub.1 through 122.sub.3, for example, resolving
power, effective minimum line width (device rule), the wavelength
of the illumination light EL (center wavelength and wavelength
width in spectrum), information about patterns to be transferred,
and other information about the projection optical system
determining the capabilities of the exposure apparatuses 122.sub.1
through 122.sub.3, which information contains some target values as
well as information about targets to be achieved by exposure
apparatuses scheduled to be introduced, e.g., information about
patterns to be transferred.
[0198] Meanwhile, the hard disk or the like of the second
communication server 130 stores an adjustment-amount computing
program (hereinafter, called a "second program" for the sake of
convenience) for computing an adjustment-amount for the imaging
characteristic based on the coefficients of terms of the Zernike
polynomial, an optimum-exposure-conditions setting program
(hereinafter, called a "third program" for the sake of convenience)
for setting optimum exposure-conditions, and a database associated
with the second program.
[0199] Next, the database will be described. The database contains
numerical data of parameters for calculating target drive amounts
(target adjustment amounts) of the movable lens devices 13.sub.1,
13.sub.2, 13.sub.4 (hereinafter, called "movable lenses"), which
amounts are for adjusting the imaging characteristic of the
projection optical system according to the measurement result of
the wave-front aberration, and, more specifically, variation
amounts of the imaging characteristics that are obtained by the
simulation using a substantially equivalent model for the
projection optical system PL of how the imaging characteristic,
e.g. the second through the 37th terms' coefficients of the Zernike
polynomial, for each of the plurality of measurement points within
the field of the projection optical system PL varies when moving
the movable lenses 13.sub.1, 13.sub.2, 13.sub.4 separately by a
unit quantity in each of directions where these are movable, the
variation amounts being arranged in the database according to a
given rule.
[0200] Next, the procedure of generating the database will be
briefly described. Exposure conditions, i.e., design values of the
projection optical system PL (numerical aperture N.A., data of
lenses, etc.) and illumination condition (coherence factor .sigma.,
the wavelength .lamda. of the illumination light, the shape of the
secondary illuminant, etc.) and then, data of a first measurement
point within the field of the projection optical system PL are
inputted into a computer for the simulation where a specific
program for calculating the optical characteristic is
installed.
[0201] Next, a unit quantity in each of directions in which movable
lenses are movable is inputted. According to, for example,
instructions to tilt the movable lens 13.sub.1 about the Y-axis
counterclockwise by a unit quantity, the computer for the
simulation calculates the deviations of a first wave-front from an
ideal wave-front for the first measurement point, for example
variations of the second term's coefficient through the 37th term's
coefficient of the Zernike polynomial, and displays the deviations
or variations on the screen thereof while storing them as parameter
PARA1P1 in memory.
[0202] Next, according to instructions to tilt the movable lens
13.sub.1 about the X-axis counterclockwise by a unit quantity, the
computer for the simulation calculates the deviations of a second
wave-front from an ideal wave-front for the first measurement
point, for example variations of the terms' coefficients of the
Zernike polynomial, and displays the deviations or variations on
the screen thereof while storing them as parameter PARA2P1 in
memory.
[0203] Next, according to instructions to shift the movable lens
13.sub.1 in the +Z direction by a unit quantity, the computer for
the simulation calculates the deviations of a third wave-front from
an ideal wave-front for the first measurement point, for example
variations of the terms' coefficients of the Zernike polynomial,
and displays the deviations or variations on the screen thereof
while storing them as parameter PARA3P1 in memory.
[0204] In the same procedure as described above, for each of the
second through n'th measurement points, the computer for the
simulation, after data of the measurement point being inputted,
calculates data of first, second and third wave-fronts, for example
variations of the terms' coefficients of the Zernike polynomial,
according to instructions to tilt the movable lens 13.sub.1 about
the X-axis, to tilt about the Y-axis and to shift in the +Z
direction respectively and displays the deviations or variations on
the screen thereof while storing them as parameters PARA1P2,
PARA2P2, PARA3P2, through PARA1Pn, PARA2Pn, PARA3Pn in memory.
[0205] Also for the other movable lenses 13.sub.2, 13.sub.3,
13.sub.4, in the same procedure as described above, for each of the
first through n'th measurement points, the computer for the
simulation, after data of the measurement point being inputted,
calculates the deviations of wave-fronts from respective ideal
wave-fronts, for example variations of the terms' coefficients of
the Zernike polynomial, according to instructions to drive the
movable lens 13.sub.2, 13.sub.3, 13.sub.4 in respective directions
where to be movable by a unit quantity and stores the deviations or
variations as parameters (PARA4P1, PARA5P1, PARA6P1, through
PARAmP1), (PARA4P2, PARA5P2, PARA6P2, through PARAmP2) through
(PARA4Pn, PARA5Pn, PARA6Pn, through PARAmPn) in memory. And a
matrix O given by the following expression (8) and composed of
column matrices (vectors) PARA1P1 through PARAmPn each of which
consists of variations of the terms' coefficients of the Zernike
polynomial stored in memory in the above manner is stored as the
database in the hard disk or the like of the second communication
server 130. In this embodiment, because there are three
three-degree-of-freedom movable lenses and a two-degree-of-freedom
movable lens, m=3.times.3+2.times.1=11. The matrix O may be
calculated for each exposure apparatus, i.e. projection optical
system, or one matrix may be for the same kind (same design values)
of projection optical systems. O = [ PARA1P1 PARA2P1 PARAmP1
PARA1P2 PARA2P2 PARAmP2 PARA1Pn PARA2Pn PARAmPn ] ( 8 )
##EQU5##
[0206] Next, the method in this embodiment of adjusting the
projection optical system PL of the exposure apparatuses 122.sub.1
through 122.sub.3 will be described. In the below, an exposure
apparatus 122 indicates any of the exposure apparatuses 122.sub.1
through 122.sub.3 unless there is a need for distinguishing
these.
[0207] As a premise, upon periodic maintenance, etc., of the
exposure apparatus 122, the main controller 50 of the exposure
apparatus 122, according to instructions of a service engineer to
measure, has measured the wave-front due to the projection optical
system PL by the wave-front-aberration measuring unit 80 and has
stored the measured wave-front data in the storage unit 42.
[0208] First, the first communication server 120 inquires at given
intervals whether or not there is measurement data of a new
wave-front (e.g. the second term's coefficient Z.sub.2 through the
37th term's coefficient Z.sub.37 of the Zernike polynomial for the
first through n'th measurement points) in the storage unit 42 of
the exposure apparatus 122. At this point of time, suppose that
measurement data of a new wave-front is stored in the storage unit
42 of the exposure apparatus 122 (in practice, any of the exposure
apparatuses 122.sub.1 through 122.sub.3). The main controller 50 of
the exposure apparatus 122 sends the measurement data of the new
wave-front to the first communication server 120 via LAN 118.
[0209] The first communication server 120 sends the measurement
data of the wave-front together with instructions to automatically
adjust the projection optical system PL (or to compute an
adjustment amount) to the second communication server 130. This
data passes through LAN 118, the first proxy server 124, and the
public telephone line 116 and reaches the second proxy server 128,
which identifies the destination address attached to the data, so
that it recognizes the data being sent to the second communication
server 130 and which sends it to the second communication server
130 via LAN 126.
[0210] The second communication server 130 receives the data and
displays its notification together with the identifier of the
source of the data on screen while storing the measurement data of
the wave-front in a hard disk or the like, and calculates an
adjustment amount of the projection optical system PL, i.e.
adjustment amounts of the movable lenses 13.sub.1 through 13.sub.4
in directions where to be movable, in the following manner.
[0211] The second communication server 130 loads the second program
into the main memory from the hard disk or the like and computes
the adjustment amounts of the movable lenses 13.sub.1 through
13.sub.4 in directions where to be movable, which computation is
specifically shown in the below.
[0212] Between data Q of the wave-front (wave-front aberration) for
the first through n'th measurement points, the matrix O contained
in the database, and an adjustment-amounts vector P of the movable
lenses 13.sub.1 through 13.sub.4 in directions where to be movable,
there exists the equation (9) Q=O.times.P. (9)
[0213] In the equation (9), P indicates a column matrix (vector)
having m elements given by the equation (10). P = [ ADJ1 ADJ2 ADJm
] ( 10 ) ##EQU6##
[0214] Therefore, computing the following equation (11) obtained
from the equation (9) with using the least-squares method gives P's
elements ADJ1 through ADJm, that is, adjustment amounts (target
adjustment amounts) of the movable lenses 13.sub.1 through 13.sub.4
in directions where to be movable
P=(O.sup.T.times.O).sup.-1.times.O.sup.T.times.Q. (11)
[0215] In the equation (11), O.sup.T and (O.sup.T.times.O).sup.-1
indicates the transposed matrix of matrix O and the inverse matrix
of (O.sup.T.times.O) respectively.
[0216] That is, the second program is one for performing a
least-squares-method computation given by the equation (11) using
the database. Therefore, the second communication server 130
calculates the adjustment amounts ADJ1 through ADJm according to
the second program while reading the database from the hard disk
into RAM.
[0217] Next, the second communication server 130 sends the
adjustment amounts ADJ1 through ADJm to the main controller 50 of
the exposure apparatus 122. By this, data containing the adjustment
amounts ADJ1 through ADJm passes through LAN 126, the second proxy
server 128, and the public telephone line 116 and reaches the first
proxy server 124, which identifies the destination address attached
to the data, so that it recognizes the data being sent to the
exposure apparatus 122 and which sends it to the exposure apparatus
122 via LAN 118. In practice, when the address attached to the data
containing the adjustment amounts ADJ1 through ADJm is AD2, AD3, or
AD4, the data is sent to the exposure apparatus 122.sub.1,
122.sub.2 or 122.sub.3 respectively.
[0218] The second communication server 130 can send the first
communication server 120 the data containing the calculated
adjustment amounts ADJ1 through ADJm, in which case the first
communication server 120 relays the data to the main controller 50
of the exposure apparatus 122 that sent the corresponding
wave-front data before.
[0219] In either case, the main controller 50 of the exposure
apparatus 122 that received the data containing the calculated
adjustment amounts ADJ1 through ADJm gives the
imaging-characteristic correcting controller 48 values specifying
drive amounts of the movable lenses 13.sub.1 through 13.sub.4 in
directions where to be movable corresponding to the adjustment
amounts ADJ1 through ADJm. The imaging-characteristic correcting
controller 48 controls the voltages applied to devices for driving
the movable lenses 13.sub.1 through 13.sub.4 in directions where to
be movable, so that at least one of the position and yaw of each of
the movable lenses 13.sub.1 through 13.sub.4 is adjusted and the
imaging characteristic of the projection optical system PL, i.e.
aberrations such as distortion, field curvature, coma, spherical
aberration, and astigmatism, is corrected. It is remarked that as
to coma, spherical aberration and astigmatism, higher orders of
aberration components can be corrected as well as lower orders of
aberration components.
[0220] As is obvious in the above description, the movable lenses
13.sub.1 through 13.sub.4, the devices for driving these movable
lenses, the imaging-characteristic correcting controller 48 and the
main controller 50 compose an imaging-characteristic adjusting
mechanism that functions as an adjusting unit in this
embodiment.
[0221] It is remarked that the first communication server 120 may
send the data containing the adjustment amounts ADJ1 through ADJm
to the imaging-characteristic correcting controller 48 via the main
controller 50 of the exposure apparatus 122 that sent the
corresponding wave-front data before so as to adjust at least one
of the position and yaw of each of the movable lenses 13.sub.1
through 13.sub.4.
[0222] In this embodiment as described above, after a service
engineer or the like attaches the wave-front-aberration measuring
unit 80 to the Z-tilt stage 58, the imaging-characteristic of the
projection optical system PL, according to instructions to measure
the wave-front aberration that are inputted via the input unit 45,
is accurately adjusted almost automatically and in a
remote-controlled manner.
[0223] While in the above description the projection optical system
is automatically adjusted, the aberrations may include one
difficult to automatically correct. In this case, a skilled
engineer on the second communication server 130's side gets
corresponding wave-front measurement data in the hard disk of the
second communication server 130 displayed on screen and analyzes it
to find out a problem, and, if an aberration difficult to
automatically correct is included, inputs an appropriate measure
through the key-board or the like of the second communication
server 130 and remotely gets it displayed on the screen of the
display unit 44 of the exposure apparatus 122. A service engineer
or the like on the maker A's side can adjust the projection optical
system by finely adjusting the positions, etc., of lenses based on
the appropriate measure on the screen in a short time.
[0224] Next, the procedure of setting the optimum exposure
conditions of the exposure apparatus 122 (122.sub.1 through
122.sub.3) will be described with reference to a flow chart of FIG.
5 showing main part of a process algorithm to be executed by the
CPU of the second communication server 130. As a premise, upon
periodic maintenance, etc., of the exposure apparatus 122.sub.1,
the main controller 50 of the exposure apparatus 122.sub.1,
according to service engineer's instructions to measure, has
already measured the wave-front aberration due to the projection
optical system PL by the wave-front-aberration measuring unit 80
and has stored the measured wave-front data in the hard disk or the
like of the first communication server 120 in the same way as
above. It is noted that although also in setting the optimum
exposure conditions data communication between the first
communication server 120 or the exposure apparatus 122.sub.1 and
the second communication server 130 is performed likewise,
explanation concerning communication and communication paths will
be omitted for the sake of simplicity.
[0225] The process in the flow chart of FIG. 5 starts when
according to instructions of an operator on the maker A's side the
first communication server 120, with specifying an exposure
apparatus whose optimum exposure conditions are to be determined,
has instructed the second communication server 130 to determine the
optimum exposure conditions and the second communication server
130, in response to this, has loaded the third program into the
main memory. The process beginning with a step 202 in FIG. 5 is
performed by executing the third program.
[0226] First, after in the step 202 it inquires conditions of the
first communication server 120, the second communication server
130, in a step 204, waits for the conditions being inputted.
[0227] During this, according to instructions of the operator to
determine the optimum exposure conditions, the first communication
server 120 inquires of, e.g., a host computer (not shown) managing
the exposure apparatuses 122.sub.1 through 122.sub.3 the
information of a reticle to be used this time by the exposure
apparatus 122.sub.1 and, based on the information of the reticle,
searches for and gets pattern information thereof from the data
base. Moreover, the first communication server 120 has inquired of
the main controller 50 of the exposure apparatus 122.sub.1
current-setting information such as an illumination condition and
has stored it in memory.
[0228] Alternatively the operator may manually input the pattern
information and information such as an illumination condition via
an input unit into the first communication server 120.
[0229] In either case, the first communication server 120 inputs
the pattern information for the simulation (e.g., in the case of a
line-and-space pattern, line widths, pitch, duty ratio, etc., or
the design data of an actual pattern) together with information of
a specified aim imaging characteristic (or an index of the imaging
characteristic; the aim imaging characteristic being called an "aim
aberration" hereinafter) and information of a line-width abnormal
value and so forth.
[0230] When the first communication server 120 has completed the
input of the conditions, the process proceeds to a step 206 in FIG.
5, which sets conditions for creating a Zernike-variations table of
the aim aberration specified in the step 204 relative to Zernike
coefficients, and then proceeds to a step 208. It is remarked that
the aim aberration information inputted in the step 204 may specify
plural kinds of aberrations in the projection optical system PL as
aim aberrations (imaging characteristic) at the same time, not
being limited to a single one.
[0231] After, in the step 208, it instructs the first communication
server 120 to input information about the projection optical system
PL of the exposure apparatus 122.sub.1, in a step 210 the second
communication server 130 waits for the input. And when the
information about the projection optical system PL, specifically a
numerical aperture N.A., an illumination condition such as setting
of the illumination-system aperture stop or coherence factor
.sigma., a wavelength, etc., has been inputted, in a step 212 the
second communication server 130 stores the inputted information in
RAM and sets specified aberration-value information, in which the
second term's coefficient Z.sub.2 through the 37th term's
coefficient Z.sub.37 of the Zernike polynomial are set such that
each term takes on, for example, a value 0.05.lamda..
[0232] A next step 214, based on the pattern information and the
information about the projection optical system PL, creates graphs
(a table of variations of, for example, a line-width abnormal value
relative to Zernike coefficients) whose ordinate is the aim
aberration (the set aberration-value information) or its index (for
example, the line-width abnormal value that is an index of coma)
and whose abscissas are corresponding terms' coefficients of the
Zernike polynomial, and the process proceeds to a step 216.
[0233] Here, the table of the variations relative to Zernike
coefficients is a table that represents sensitivities (Zernike
Sensitivity), to a specific aberration, i.e. the aim aberration (or
its index), of coefficients of terms of the Zernike polynomial in
which the wave-front in the projection optical system is expanded,
the aberration being measured with respect to the pattern given as
an object pattern, and is uniquely defined based on the pattern
information, the information about the projection optical system
PL, and the set aberration-value information as well as, for the
same kind of projection optical systems, based on design
information containing the kind and configuration of lens devices
composing the projection optical system. Therefore, by searching in
the in-house database of the maker B for and identifying the kind
of the projection optical system of an exposure apparatus
specified, for example by product name, as an object whose optimum
exposure conditions is to be determined, the Zernike-variations
table can be created.
[0234] A next step 216 checks whether or not Zernike-variations
tables for all the aim aberrations specified in the step 204 have
been created. If the answer is NO, the process returns to the step
214, and the Zernike-variations table for a next aim aberration is
created.
[0235] After Zernike-variations tables for all the aim aberrations
have been created, and the answer in the step 216 becomes YES, the
process proceeds to a next step 218. After, in the step 218, it
instructs the first communication server 120 to input measurement
data of the wave-front, in a step 220 the second communication
server 130 waits for the input of the measurement data. When the
first communication server 120 has inputted from its hard disk the
measurement data of the wave-front (for example, the second term's
coefficient Z.sub.2 through the 37th term's coefficient Z.sub.37 of
the Zernike polynomial for wave-fronts for the first through n'th
measurement points), in a next step 222 the second communication
server 130 performs, for each measurement point, computation given
by the following equation (12) using the created Zernike-variations
tables in order to obtain and store one of the aim aberrations,
specified in the step 204, in RAM A=K.times.{Z.sub.2.times.(a
table's value)+Z.sub.3.times.(a table's value)+ . . .
+Z.sub.37.times.(a table's value)}. (12)
[0236] Here, A indicates an aim aberration in the projection
optical system PL such as astigmatism or field curvature, or an
index of the aim aberration such as a line-width abnormal value
that is an index of coma, and K is a proportional constant
depending on the sensitivity of the resist and so forth.
[0237] When A indicates the line-width abnormal value, and the
pattern is a line-and-space pattern having five lines therein for
example, the line-width abnormal value is given by the above
equation (1). As is obvious in the equation (1), the calculation of
the equation (12) is one for converting the pattern into space
images (projected images).
[0238] A next step 224 checks whether or not all the aim
aberrations (aberrations (imaging characteristic) for which
conditions were set) have been calculated. If the answer is NO, the
process returns to the step 222, and a next aim aberration is
calculated and stored in RAM.
[0239] When all the aim aberrations have been calculated, in a step
226 the calculation results of all the aim aberrations in RAM are
stored in the hard disk or the like, and the process proceeds to a
next step 228.
[0240] In the step 228, after the information about the projection
optical system PL, specifically a numerical aperture N.A., an
illumination condition such as setting of the illumination-system
aperture stop or coherence factor .sigma., a wavelength, etc., has
been changed partly compared to the one given in the step 210, in a
step 230 the second communication server 130 checks whether or not
the information has been changed a predetermined number of times.
At this point of time, because the information about the projection
optical system PL has been changed only once, the answer is NO, and
after the process returns to the step 214, the process of the steps
214 through 230 is repeated, in the step 214 of which
Zernike-variations tables are created based on the information
about the projection optical system PL that has been changed in the
step 228. In this manner, the process of the steps 214 through 230
is repeated each time with partly different illumination condition,
numerical aperture, wavelength, etc. After the process has been
repeated the predetermined number of times, the answer in the step
230 becomes YES, and the process proceeds to a next step 232. At
this point of time, the calculation results of the aim aberrations
for the predetermined number of conditions settings are stored in
the hard disk or the like.
[0241] In the step 232, the second communication server 130
determines conditions (an illumination condition, a numerical
aperture, a wavelength, etc.) concerning the projection optical
system, under which the aim aberrations stored in the hard disk or
the like take on optimum values (for example, zero or minimum), as
optimum exposure conditions.
[0242] In a next step 234, data containing the optimum exposure
conditions are sent to the first communication server 120, and the
process of this routine ends.
[0243] The first communication server 120, which has received the
data containing the optimum exposure conditions, instructs, as
needed, the main controller 50 of the exposure apparatus 122.sub.1
to set its exposure conditions to the optimum exposure conditions.
Specifically, the main controller 50 can change and set the
illumination condition by changing the aperture stop of the
illumination-system aperture stop plate 24, can adjust the
numerical aperture of the projection optical system PL by adjusting
the aperture stop 15 of the projection optical system PL shown in
FIG. 2, and can set the wavelength of exposure light by giving the
light source 16 control information TS to change the wavelength of
the illumination light EL.
[0244] It is noted that the second communication server 130 may
directly instruct the exposure apparatus 122.sub.1 to set its
exposure conditions to the optimum exposure conditions.
[0245] Moreover, by making a slight modification to the third
program whose process is shown by the flow chart in FIG. 5, a
process is given where the steps of creating Zernike-variations
tables and calculating aim aberrations (or space images) based on
wave-front measurement data in the same way as described above
while little by little changing the pattern information with the
other setting information fixed are repeated to determine optimum
pattern information as optimum exposure conditions.
[0246] Likewise, by making a slight modification to the third
program whose process is shown by the flow chart in FIG. 5, a
process is given where the steps of creating Zernike-variations
tables and calculating aim aberrations (or space images) based on
wave-front measurement data in the same way as described above
while little by little changing the specified-aberration-value
information with the other setting information fixed are repeated
to determine optimum aberration-value information of the projection
optical system upon transferring the given pattern as optimum
exposure conditions. In this case the second communication server
130 adjusts the imaging characteristic by controlling the
imaging-characteristic correcting controller 48 via the main
controller 50 of the exposure apparatus 122.sub.1 such that the
aberration due to the projection optical system PL (for example,
the second term's coefficient Z.sub.2 through the 37th term's
coefficient Z.sub.37 of the Zernike polynomial) takes on the
optimum aberration-value. Alternatively the second communication
server 130 may adjust the imaging characteristic by controlling the
imaging-characteristic correcting controller 48 via the first
communication server 120 and the main controller 50 such that the
aberration due to the projection optical system PL takes on the
optimum aberration-value.
[0247] Optimum exposure conditions of the exposure apparatuses
122.sub.2, 122.sub.3 are set in the same way as described
above.
[0248] In this embodiment, upon periodic maintenance, etc., of the
exposure apparatus 122, when a service engineer inputs condition
settings, information about the projection optical system, etc.,
through the first communication server 120, the second
communication server 130 creates Zernike-variations tables using
another program partly different from the third program in the same
way as the simulation for setting optimum exposure conditions. And
the main controller 50 of the exposure apparatus 122, according to
instructions of the service engineer, measures the wave-front
aberration and sends position deviations data obtained from the
measurement via the first communication server 120 to the second
communication server 130, which calculates the aim aberration in
the same way as described above and drive amounts of the movable
lenses 13.sub.1 through 13.sub.4 in directions where to be movable
which amounts make the aim aberration optimal (e.g. zero or
minimal), by using the another program and the least-squares
method. And the second communication server 130 supplies the drive
amounts to the imaging-characteristic correcting controller 48 via
the main controller 50, according to which the
imaging-characteristic correcting controller 48 controls voltages
applied to the devices for driving the movable lenses 13.sub.1
through 13.sub.4 in directions where to be movable, so that at
least one of the position and yaw of each of the movable lenses
13.sub.1 through 13.sub.4 is adjusted and that the aim aberration
of the projection optical system PL such as distortion, field
curvature, coma, spherical aberration, astigmatism, etc., is
corrected. It is remarked that as to coma, spherical aberration and
astigmatism, higher orders of aberration components can be
corrected as well as lower orders of aberration components. In this
case the second program is not necessarily used.
[0249] Moreover, in this embodiment when the another program partly
different from the third program is installed in the storage unit
42 from the driving unit 46, automatic adjustment of the imaging
characteristic of the projection optical system PL by the exposure
apparatus 122 itself upon adjustment of the projection optical
system PL of the exposure apparatus 122 such as periodic
maintenance is easily achieved. In this case, according to
instructions of an operator (with condition settings, information
about the projection optical system, etc., inputted), the CPU of
the main controller 50 performs the same process in the same way as
in the above simulation, to create the same Zernike-variations
tables. And after position deviations data obtained by measuring
the wave-front aberration has been inputted, the CPU of the main
controller 50 calculates the aim aberration in the same way as
described above and then drive amounts of the movable lenses
13.sub.1 through 13.sub.4 in directions where to be movable which
amounts make the aim aberration optimal (e.g. zero or minimal), by
using the another program and the least-squares method. And the CPU
of the main controller 50 supplies the drive amounts to the
imaging-characteristic correcting controller 48, according to which
the imaging-characteristic correcting controller 48 controls
voltages applied to the devices for driving the movable lenses
13.sub.1 through 13.sub.4 in directions where to be movable, so
that at least one of the position and yaw of each of the movable
lenses 13.sub.1 through 13.sub.4 is adjusted and the aim aberration
of the projection optical system PL such as distortion, field
curvature, coma, spherical aberration, astigmatism, etc., is
corrected. It is remarked that as to coma, spherical aberration and
astigmatism, higher orders of components can be corrected as well
as lower orders of components.
[0250] As is obvious in the above description, the movable lenses
13.sub.1 through 13.sub.4, the devices for driving these movable
lenses, and the imaging-characteristic correcting controller 48
compose an imaging-characteristic adjusting mechanism which
functions as an adjusting unit in this embodiment and which is
controlled by the main controller 50.
[0251] It is noted that while the wave-front-aberration measuring
unit 80 measures the wave-front aberration due to the projection
optical system PL in the above description, not being limited to
this, the wave-front aberration may be measured by using a
measurement reticle R.sub.T described below (hereinafter, also
called a "reticle R.sub.T" as needed).
[0252] FIG. 6 shows a schematic oblique view of the measurement
reticle R.sub.T, and FIG. 7 shows a schematic view of the cross
section of the reticle R.sub.T along a X-Z plane near the optical
axis AX and a diagram of the projection optical system PL. FIG. 8
shows a schematic view of the cross section of the reticle R.sub.T
along a X-Z plane near the end in the -Y side and a diagram of the
projection optical system PL.
[0253] As is obvious in FIG. 6, the measurement reticle R.sub.T has
almost the same shape as a usual reticle with a pellicle and
comprises a glass substrate 60, a lens-attaching member 62 having a
rectangular-plate-like shape and which is fixed on the upper
surface of the glass substrate 60 in FIG. 6 such that its center
coincides with that of the glass substrate 60, a spacer member 64
constituted by a frame member fixed on the bottom surface of the
glass substrate 60 in FIG. 6 and having the same shape as a usual
pellicle frame, and an aperture plate 66 fixed on the bottom
surface of the spacer member 64.
[0254] In the lens-attaching member 62, a matrix arrangement of n
circular apertures 63.sub.i,j (i=1 through p, j=1 through q,
p.times.q=n) is formed which covers the other part of the surface
than both the ends in the Y-direction. Provided inside of the
circular apertures 63.sub.i,j are condenser lenses 65.sub.i,j each
constituted by a convex lens whose optical axis is parallel to the
Z-direction (refer to FIG. 7).
[0255] Inside the space enclosed by the glass substrate 60, the
spacer member 64 and the aperture plate 66, supporting members 69
are arranged spaced a predetermined distance apart from each other
as shown in FIG. 7.
[0256] Furthermore, measurement patterns 67.sub.i,j are formed on
the opposite side of the glass substrate 60 to the condenser lenses
65.sub.i,j as shown in FIG. 7. Made opposite the measurement
patterns 67.sub.i,j in the aperture plate 66 as shown in FIG. 7 are
pinhole-like openings 70.sub.i,j, whose diameter is, for example,
about 100 to 150 um.
[0257] Referring back to FIG. 6, openings 72.sub.1, 72.sub.2 are
made in center of the band areas in the ends in the Y-direction of
the lens-attaching member 62 respectively. A reference pattern
74.sub.1 is formed opposite the opening 72.sub.1 on the bottom
surface (pattern surface) of the glass substrate 60 as shown in
FIG. 8. Although not shown, a reference pattern 74.sub.2 identical
to the reference pattern 74.sub.1 is formed opposite the other
opening 72.sub.2 on the bottom surface (pattern surface) of the
glass substrate 60.
[0258] Moreover, as shown in FIG. 6, a pair of reticle alignment
marks RM1, RM2 is formed symmetrically with respect to the
reticle's center, on the center line parallel to the X-direction of
the glass substrate 60 and outside the lens-attaching member
62.
[0259] Here, in this embodiment, the measurement patterns
67.sub.i,j are a mesh (street-lines-like) pattern as shown in FIG.
9A. Corresponding to these, the reference patterns 74.sub.1,
74.sub.2 are a two-dimensional pattern with square features
arranged at the same pitch as the measurement pattern 67.sub.i,j as
shown in FIG. 9B. It is remarked that the reference pattern
74.sub.1, 74.sub.2 may be the pattern of FIG. 9A while the
measurement pattern is the pattern of FIG. 9B. Furthermore, the
measurement pattern 67.sub.i,j may be a pattern having a different
shape, in which case the corresponding reference pattern needs to
be a pattern having a predetermined positional relation with the
measurement pattern. That is, the reference pattern only has to be
a pattern providing the reference for position deviation of the
measurement pattern. Whatever the shape thereof is, the pattern
preferably covers the whole image field or exposure area of the
projection optical system PL in order to measure the imaging
characteristic of the projection optical system PL.
[0260] Next, the measurement of the wave-front aberration due to
the projection optical system PL of the exposure apparatus 122 (the
exposure apparatus 122.sub.1 through 122.sub.3) using the reticle
R.sub.T will be described.
[0261] First the wave-front aberration is measured for a plurality
of measurement points (herein, n points) within the field of the
projection optical system PL using the measurement reticle R.sub.T
in the following manner.
[0262] When an operator (or a service engineer) has inputted an
instruction to measure the wave-front aberration through the input
unit 45, the main controller 50 loads the measurement reticle
R.sub.T onto the reticle stage RST via a reticle loader (not
shown), and moves the wafer stage WST via the wafer-stage driving
portion 56 with monitoring the output of the laser interferometer
54W such that a pair of reticle alignment reference marks on the
reference mark plate FM is positioned at a predetermined reference
position, specifically for example, such that the center of the
pair of reference marks coincides with the origin of the stage
coordinate system defined by the laser interferometer 54W.
[0263] Next, while simultaneously observing a pair of reticle
alignment marks RM1, RM2 on the measurement reticle R.sub.T and the
reticle alignment reference marks corresponding thereto using the
reticle alignment microscopes, the main controller 50 finely drives
the reticle stage RST along the X-Y two-dimensional plane via a
driving system (not shown) such that position deviations of
projected images on the reference plate FM of the reticle alignment
marks RM1, RM2 from the reference marks becomes minimal. By this,
reticle alignment is completed, and the center of the reticle
almost coincides with the optical axis of the projection optical
system PL.
[0264] Next, the main controller 50 loads a wafer W whose surface
is coated with a resist (photosensitive material) onto the Z-tilt
stage 58 via a wafer loader (not shown).
[0265] Then, the main controller 50 sets the aperture size of the
reticle blind 30 in order to form a rectangular illumination area
which covers all the condenser lenses 65.sub.i,j of the measurement
reticle R.sub.T but not the openings 72.sub.1, 72.sub.2 and which
has an X-direction length not larger than the maximum width in the
X-direction of the lens-attaching member 62. At the same time, the
main controller 50 rotates the illumination-system aperture stop
plate 24 via the driving unit 40 to put a specified aperture stop,
for example the small .sigma. stop, on the optical path of the
illumination light EL.
[0266] After that preparation, the main controller 50 supplies
control information TS to the light source 16 to make it generate
laser beam LB and illuminate and expose the reticle R.sub.T to the
illumination light EL. By this, as shown in FIG. 7, the measurement
patterns 67.sub.i,j are simultaneously transferred through the
pinhole-like openings 70.sub.i,j and the projection optical system
PL. As a result, the reduced images 67'.sub.i,j (latent images) of
the measurement patterns 67.sub.i,j, as shown in FIG. 10A, are
formed spaced a predetermined distance apart from each other
two-dimensionally on the resist layer on the wafer W.
[0267] Next, the main controller 50 moves the reticle stage RST in
the Y-direction by a predetermined distance via a driving system
(not shown) based on a measurement value of a reticle laser
interferometer and positional relation planned in design between
the reticle's center and the reference pattern 74.sub.1 such that
the center of the reference pattern 74.sub.1 is placed on the
optical axis AX. Next, the main controller 50 sets the aperture of
the reticle blind 30 via a driving system (not shown) such that the
illumination light EL only illuminates a rectangular area having a
predetermined size on the lens-attaching member 62 and including
the opening 72.sub.1 (but not any condenser lens).
[0268] Then the main controller 50 moves the wafer stage WST with
monitoring measurement values of the laser interferometer 54W such
that the center of the latent image 67'.sub.1,1 on the wafer W of
the first measurement pattern 67.sub.1,1 is placed almost on the
optical axis AX.
[0269] Then the main controller 50 supplies control information TS
to the light source 16 to make it generate laser beam LB and
illuminate and expose the reticle R.sub.T to the illumination light
EL. By this, the reference pattern 74.sub.1 is transferred and
overlaid onto the area where the latent image of the measurement
pattern 67.sub.1,1 is already formed on the resist layer on the
wafer W, the area being called an area S.sub.1,1. As a result, the
latent images 67'.sub.1,1 and 74'.sub.1 of the first measurement
pattern 67.sub.1,1 and the reference pattern 74.sub.1 are formed on
the area S.sub.1,1 in a positional relation as shown in FIG.
10B.
[0270] Next, the main controller 50 calculates the arrangement
pitch P of the measurement patterns 67.sub.i,j on the wafer W,
which pitch P is planned in design, based on the arrangement pitch
of the measurement patterns 67.sub.i,j on the reticle R.sub.T and
the projection magnification of the projection optical system PL
and moves the wafer stage WST in the X-direction by the pitch P
such that the center of an area S.sub.1,2 where the latent image of
the second measurement pattern 67.sub.1,2 is formed is placed
almost on the optical axis AX.
[0271] Then the main controller 50 supplies control information TS
to the light source 16 to make it generate laser beam LB and
illuminate and expose the reticle R.sub.T to the illumination light
EL. By this, the reference pattern 74.sub.1 is transferred and
overlaid onto the area S.sub.1,2 on the wafer W.
[0272] After that, stepping likewise between the areas and exposure
are repeated, so that latent images, as shown in FIG. 10B, of the
measurement patterns and the reference pattern are formed in the
areas S.sub.i,j on the wafer W.
[0273] After the completion of exposure, the main controller 50
unloads the wafer W from the Z-tilt stage 58 via the wafer loader
(not shown) and transfers the wafer to a coater-developer (not
shown; hereinafter, "C/D" for short) connected in-line with the
chamber 11, which C/D develops the wafer W, so that the resist
images, each having the same arrangement as shown in FIG. 10B, of
the measurement patterns and the reference pattern are formed in
the areas S.sub.i,j arranged in a matrix on the wafer W.
[0274] After that, the wafer W already developed is removed from
the C/D and an external overlay measuring unit (registration
measuring unit) measures overlay errors in the areas S.sub.i,j.
Based on the result, position errors (position deviations) of the
resist images of the measurement patterns 67.sub.i,j from the
corresponding reference pattern 74.sub.1 are calculated. It is
remarked that while there are various methods of calculating the
position deviations, statistical computation is preferably employed
based on measured raw data in terms of improving accuracy.
[0275] In this manner, for the areas S.sub.i,j, X-Y-two-dimensional
position deviations (.DELTA..xi.', .DELTA..eta.') of the
measurement patterns from the corresponding reference patterns are
obtained, which are inputted into the main controller 50 through
the input unit 45 by the service engineer or the like. It is
remarked that the external overlay measuring unit may input the
position deviations (.DELTA..xi.', .DELTA..eta.') in the areas
S.sub.i,j into the main controller 50 through the network.
[0276] In either case, responding to the input the CPU of the main
controller 50 loads the similar computing program to the first
program, and, based on the position deviations (.DELTA..xi.',
.DELTA..eta.'), computes the wave-fronts (wave-front aberrations)
for the areas S.sub.i,j, that is, the first through n'th
measurement points within the field of the projection optical
system PL, specifically, the second term's coefficient Z.sub.2
through the 37th term's coefficient Z.sub.37 of the Zernike
polynomial by using the computing program.
[0277] Here, the physical relation between the position deviations
(.DELTA..xi.', .DELTA..eta.') and the wave-front will be briefly
described with reference to FIGS. 7 and 8, which is a premise for
the computation based on the position deviations (.DELTA..xi.',
.DELTA..eta.') which the CPU of the main controller 50 performs to
obtain the wave-front in the projection optical system PL.
[0278] As represented by a measurement pattern 67.sub.k,l in FIG.
7, one of sub-beams diffracted by a measurement pattern 67.sub.i,j
passes through a respective pinhole-like opening 70.sub.i,j and
then the pupil plane of the projection optical system PL in a
different position depending on the position of the measurement
pattern 67.sub.i,j. That is, wave-front's part in each position on
the pupil plane mainly reflects the wave-front of the sub-beam from
the corresponding measurement pattern 67.sub.i,j. If the projection
optical system PL caused no aberration, the wave-front on the pupil
plane of the projection optical system PL would become an ideal one
(herein, a flat plane) indicated by a numerical reference F.sub.1.
However, because projection optical systems that cause no
aberration do not exist, the wave-front on the pupil plane becomes
a curved surface F.sub.2 represented by a dotted curve for example.
Therefore, the measurement pattern 67.sub.i,j is imaged in a
position on the wafer W that deviates according to the angle that
the curved surface F.sub.2 makes with the ideal wave-front.
[0279] Meanwhile, light diffracted by the reference pattern
74.sub.1 (or 74.sub.2), as shown in FIG. 8, is not restricted by a
pinhole-like aperture, is made incident directly on the projection
optical system PL and is imaged on the wafer W through the
projection optical system PL. Moreover, because exposure of the
reference pattern 74.sub.1 is performed in a state where the center
of the reference pattern 74.sub.1 is positioned on the optical axis
of the projection optical system PL, almost no aberration of the
imaging beam from the reference pattern 74.sub.1 is caused by the
projection optical system PL, so that the image is formed with no
position deviation on a small area that the optical axis passes
through.
[0280] Therefore, the position deviations (.DELTA..xi.',
.DELTA..eta.') directly reflect the tilts of the wave-front to an
ideal wave-front, and based on the position deviations
(.DELTA..xi.', .DELTA..eta.') the wave-front can be drawn. It is
noted that as physical relation between the position deviations
(.DELTA..xi.', .DELTA..eta.') and the wave-front indicates, the
principle of this embodiment for calculating the wave-front is the
known Shack-Hartmann wave-front calculation principle.
[0281] Disclosed in U.S. Pat. No. 5,978,085 is an invention
concerning the technology where a plurality of measurement patterns
on a mask having the same structure as the measurement reticle
R.sub.T are sequentially imaged on a substrate through respective
pinholes and a projection optical system, where a reference pattern
on the mask is imaged on the substrate through the projection
optical system but not through condenser lenses and the pinholes,
and where position deviations of the resist images of the plurality
of measurement patterns from the respective resist images of the
reference pattern are measured to calculate the wave-front
aberration by a predetermined computation.
[0282] Incidentally, when semiconductor devices are manufactured
using the exposure apparatuses 122.sub.1 through 122.sub.3 of this
embodiment, preparation such as reticle alignment, so-called
base-line measurement and EGA (Enhanced Global Alignment) is
perforemed after a reticle R for manufacturing the devices is
loaded onto the reticle stage RST.
[0283] The above preparation such as reticle alignment and
base-line measurement is disclosed in detail in, for example,
Japanese Patent Laid-Open No. 4-324923 and U.S. Pat. No. 5,243,195
corresponding thereto. Furthermore, the EGA is disclosed in detail
in, for example, Japanese Patent Laid-Open No. 61-44429 and U.S.
Pat. No. 4,780,617 corresponding thereto. The disclosures in the
above U.S. Patents are incorporated herein by reference as long as
the national laws in designated states or elected states, to which
this international application is applied, permit.
[0284] After that, exposure of the step-and-repeat type as in the
measurement of the wave-front aberration using the measurement
reticle R.sub.T is performed, in which stepping is performed based
on the result of wafer alignment. Because the exposure operation is
the same as in a usual stepper, its detailed description is
omitted.
[0285] Next, the method of making the projection optical system PL
in the making of the exposure apparatus 122 (122.sub.1 through
122.sub.3) will be described.
[0286] a. Determining the Specification for the Projection Optical
System PL
[0287] An engineer or the like of the maker A inputs into the first
communication server 120 via its input unit (not shown) target
information for the exposure apparatus such as an exposure
wavelength, a minimum line width (resolution) and information
regarding a pattern to be exposed, and instructs the first
communication server 120, via its input unit, to send the target
information.
[0288] The first communication server 120 inquires of the second
communication server 130 whether or not it can receive data, and,
when the second communication server 130 replies that it can
receive data, sends the target information to the second
communication server 130.
[0289] The second communication server 130 receives and analyzes
the target information, selects based on the result of the analysis
one of seven methods described later for determining the
specification, and determines and stores the specification in
RAM.
[0290] Here, before explaining the methods of determining the
specification, what aberrations the terms of the Zernike polynomial
(fringe Zernike polynomial) in which the wave-front is expanded are
associated with will be briefly described. Each term includes the
function f.sub.i(.rho.,.theta.) as shown in table 1 and is a term
of n'th order and m.theta., where n indicates the maximum power of
.rho. and m the coefficient of .theta..
[0291] The 0 order, 0.theta. term (coefficient Z.sub.1) represents
the position of the wave-front and is not associated with any
aberration.
[0292] The first order, 1.theta. term (coefficients Z.sub.2,
Z.sub.3) represents the distortion component.
[0293] The second order, 0.theta. term (coefficient Z.sub.4)
represents the field curvature.
[0294] The third and over order, 0.theta. terms (coefficients
Z.sub.g, Z.sub.16, Z.sub.25, Z.sub.36, Z.sub.37) represent the
spherical aberration component.
[0295] The 2.theta. terms (coefficients Z.sub.5, Z.sub.6, Z.sub.12,
Z.sub.13, Z.sub.21, Z.sub.22, Z.sub.32, Z.sub.33) and the 4.theta.
terms (coefficients Z.sub.17, Z.sub.18, Z.sub.28, Z.sub.29)
represent the astigmatism component.
[0296] The third and over order, 1.theta. terms (coefficients
Z.sub.7, Z.sub.8, Z.sub.14, Z.sub.15, Z.sub.23, Z.sub.24, Z.sub.34,
Z.sub.35), the third and over order, 3.theta. terms (coefficients
Z.sub.10, Z.sub.11, Z.sub.19, Z.sub.20, Z.sub.30, Z.sub.31) and the
5.theta. terms (coefficient Z.sub.26, Z.sub.27) represent the coma
component.
[0297] The seven methods of determining the specification with
using as a standard the wave-front aberration amount that the
projection optical system PL is to satisfy will be described in the
below.
<A First Method>
[0298] In this method, the coefficients of terms specified by the
target information out of the terms of the Zernike polynomial in
which the wave-front in the projection optical system is expanded
are selected as standards. In the first method, with using, e.g.,
the coefficients Z.sub.2, Z.sub.3 corresponding to the distortion
component as standards when the target information contains a
resolving power for example, the specification of the projection
optical system PL is determined such that the coefficients within
the field are at or below respective, predetermined values.
<A Second Method>
[0299] In this method, with using the RMS value (Root-Mean-Square
value) of the coefficients of the terms of the Zernike polynomial
in which the wave-front in the projection optical system is
expanded as a standard, the specification of the projection optical
system PL is determined such that the RMS value within the field is
not larger than a given limit. By the second method field
curvature, etc., can be constrained. The second method can be
suitably applied to any target information. Alternatively, for each
coefficient the RMS value of its values within the field may be
used as a standard.
<A Third Method>
[0300] In this method, with selecting as standards the coefficients
of the terms of the Zernike polynomial in which the wave-front in
the projection optical system is expanded, the specification of the
projection optical system PL is determined such that the
coefficients within the field are at or below respective, given
limits. In the third method the limits may all be the same in value
or different from each other, or some of the limits may be the same
in value.
<A Fourth Method>
[0301] In this method, with using as a standard the RMS value,
within the field, of the coefficients of terms (n'th order,
m.theta. terms), which correspond to a given aberration, out of the
terms of the Zernike polynomial in which the wave-front in the
projection optical system is expanded, the specification of the
projection optical system PL is determined such that the RMS value
is not larger than a given limit. In the fourth method when the
target information contains pattern information, based on a
presumption, obtained from the pattern information, which
aberration must particularly be restricted in order to form a good
projected image of the pattern on the image plane, the limits for
the RMS values of the coefficients of n'th order, m.theta. terms
are determined, for example, as follows.
[0302] Let the RMS value A.sub.1 of the coefficients Z.sub.2,
Z.sub.3 within the field be a standard, then the standard
A.sub.1.ltoreq.limit B.sub.1.
[0303] Let the RMS value A.sub.2 of the coefficient Z.sub.4 within
the field be a standard, then the standard A.sub.2.ltoreq.limit
B.sub.2.
[0304] Let the RMS value A.sub.3 of the coefficients Zs, Z.sub.6
within the field be a standard, then the standard
A.sub.3.ltoreq.limit B.sub.3.
[0305] Let the RMS value A.sub.4 of the coefficients Z.sub.7,
Z.sub.8 within the field be a standard, then the standard
A.sub.4.ltoreq.limit B.sub.4.
[0306] Let the RMS value A.sub.S of the coefficient Z.sub.9 within
the field be a standard, then the standard A.sub.5.ltoreq.limit
B.sub.5.
[0307] Let the RMS value A.sub.6 of the coefficients Z.sub.10,
Z.sub.11 within the field be a standard, then the standard
A.sub.6.ltoreq.limit B.sub.6.
[0308] Let the RMS value A.sub.7 of the coefficients Z.sub.12,
Z.sub.13 within the field be a standard, then the standard
A.sub.7.ltoreq.limit B.sub.7.
[0309] Let the RMS value A.sub.8 of the coefficients Z.sub.14,
Z.sub.15 within the field be a standard, then the standard
A.sub.8.ltoreq.limit B.sub.8.
[0310] Let the RMS value A.sub.9 of the coefficient Z.sub.16 within
the field be a standard, then the standard A.sub.9.ltoreq.limit
B.sub.9.
[0311] Let the RMS value A.sub.10 of the coefficients Z.sub.17,
Z.sub.18 within the field be a standard, then the standard
A.sub.10.ltoreq.limit B.sub.10.
[0312] Let the RMS value A.sub.11 of the coefficients Z.sub.19,
Z.sub.20 within the field be a standard, then the standard
A.sub.11.ltoreq.limit B.sub.11.
[0313] Let the RMS value A.sub.12 of the coefficients Z.sub.21,
Z.sub.22 within the field be a standard, then the standard
A.sub.12.ltoreq.limit B.sub.12.
[0314] Let the RMS value A.sub.13 of the coefficients Z.sub.23,
Z.sub.24 within the field be a standard, then the standard
A.sub.13.ltoreq.limit B.sub.13.
[0315] Let the RMS value A.sub.14 of the coefficient Z.sub.25
within the field be a standard, then the standard
A.sub.14.ltoreq.limit B.sub.14.
[0316] Let the RMS value A.sub.15 of the coefficients Z.sub.26,
Z.sub.27 within the field be a standard, then the standard
A.sub.15.ltoreq.limit B.sub.15.
[0317] Let the RMS value A.sub.16 of the coefficients Z.sub.28,
Z.sub.29 within the field be a standard, then the standard
A.sub.16.ltoreq.limit B.sub.16.
[0318] Let the RMS value A.sub.17 of the coefficients Z.sub.30,
Z.sub.31 within the field be a standard, then the standard
A.sub.17.ltoreq.limit B.sub.17.
[0319] Let the RMS value A.sub.18 of the coefficients Z.sub.32,
Z.sub.33 within the field be a standard, then the standard
A.sub.18.ltoreq.limit B.sub.18.
[0320] Let the RMS value A.sub.19 of the coefficients Z.sub.34,
Z.sub.35 within the field be a standard, then the standard
A.sub.19.ltoreq.limit B.sub.19.
[0321] Let the RMS value A.sub.20 of the coefficients Z.sub.36,
Z.sub.37 within the field be a standard, then the standard
A.sub.20.ltoreq.limit B.sub.20.
<A Fifth Method>
[0322] In a fifth method, with using as a standard the RMS value,
within the field, of the coefficients of each group of m.theta.
terms having the same m.theta. value out of terms, which correspond
to a given aberration, out of the terms of the Zernike polynomial
in which the wave-front in the projection optical system is
expanded, the specification of the projection optical system PL is
determined such that the RMS value for each group is not larger
than a respective, given limit.
[0323] For example, let the RMS value C.sub.1, within the field, of
the coefficients Z.sub.9, Z.sub.16, Z.sub.25, Z.sub.36, Z.sub.37 of
the third and over order, 0.theta. terms be a standard, then the
standard C.sub.1.ltoreq.limit D.sub.1.
[0324] Let the RMS value C.sub.2, within the field, of the
coefficients Z.sub.7, Z.sub.8, Z.sub.14, Z.sub.15, Z.sub.23,
Z.sub.24, Z.sub.34, Z.sub.35 of the third and over order, 1.theta.
terms be a standard, then the standard C.sub.2.ltoreq.limit
D.sub.2.
[0325] Let the RMS value C.sub.3, within the field, of the
coefficients Z.sub.5, Z.sub.6, Z.sub.12, Z.sub.13, Z.sub.21,
Z.sub.22, Z.sub.32, Z.sub.33 of the 2.theta. terms be a standard,
then the standard C.sub.3.ltoreq.limit D.sub.3.
[0326] Let the RMS value C.sub.4, within the field, of the
coefficients Z.sub.10, Z.sub.11, Z.sub.19, Z.sub.20, Z.sub.30,
Z.sub.31 of the 3.theta. terms be a standard, then the standard
C.sub.4.ltoreq.limit D.sub.4.
[0327] Let the RMS value C.sub.5, within the field, of the
coefficients Z.sub.17, Z.sub.18, Z.sub.28, Z.sub.29 of the 4.theta.
terms be a standard, then the standard C.sub.5.ltoreq.limit
D.sub.5.
[0328] Let the RMS value C.sub.6, within the field, of the
coefficients Z.sub.26, Z.sub.27 of the 5.theta. terms be a
standard, then the standard C.sub.6.ltoreq.limit D.sub.6.
[0329] Also in this method, as is obvious from the meanings of the
coefficients, when the target information contains pattern
information, based on a presumption, obtained from the pattern
information, which aberration must particularly be restricted in
order to form a good projected image of the pattern on the image
plane, a standard is selected.
<A Sixth Method>
[0330] In a sixth method, with using a given standard of the RMS
value, within the field, of coefficients given by weighting
according to the target information the coefficients of the terms
of the Zernike polynomial in which the wave-front in the projection
optical system is expanded, the specification of the projection
optical system is determined such that the RMS value is not larger
than a given limit. Also in this method when the target information
contains pattern information, based on a presumption, obtained from
the pattern information, which aberration must particularly be
restricted in order to form a good projected image of the pattern
on the image plane, the weights are determined.
<A Seventh Method>
[0331] A seventh method can be employed only when the target
information contains information about a pattern that the
projection optical system projects, and by analyzing the result of
a simulation for, based on the pattern information, obtaining a
space image formed on the image plane when the projection optical
system projects the pattern, the specification of the projection
optical system is determined using as a standard the wave-front
aberration amount allowed for the projection optical system such
that the pattern is transferred finely. In the simulation, based on
linear combinations between sensitivities (Zernike Sensitivity) of
the coefficients of the terms of the Zernike polynomial in which
the wave-front in the projection optical system is expanded, to a
given aberration (or an index) for the pattern (object pattern) and
the coefficients of the terms of the Zernike polynomial, the space
image may be obtained which sensitivities are given from
Zernike-variations tables which were created beforehand in the same
way as above, the sensitivities depending on said pattern.
[0332] This will be described in more detail below. There exists a
relation given by the following equation (13) between a matrix f
with n rows and m columns that comprises data of various
aberrations (or their indexes) in n measurement points within the
field of the projection optical system, for example, m kinds of
aberrations and a matrix Wa with n rows and 36 columns that
comprises the wave-front aberration data for n measurement points,
for example, terms' coefficients (e.g. the second term's
coefficient Z.sub.2 through the 37th term's coefficient Z.sub.37)
of the Zernike polynomial in which the wave-front aberration is
expanded and a Zernike-variations table, i.e., a matrix ZS with,
e.g., 36 rows and m columns that comprises variation (Zernike
Sensitivity) per 1.lamda. in each of the coefficients (e.g. Z.sub.2
through Z.sub.37) of Zernike polynomial's terms corresponding to m
kinds of aberrations under given exposure conditions:
f=Wa.times.ZS. (13)
[0333] Here, f, Wa, and ZS are represented by, for example, the
equations (14), (15), (16) respectively: f = [ f 1 , 1 f 1 , 2 f 1
, m f 2 , 1 f 2 , m f n , 1 f n , 2 f n , m ] ( 14 ) Wa = [ Z 1 , 2
Z 1 , 3 Z 1 , 36 Z 1 , 37 Z 2 , 2 Z 2 , 37 Z n , 2 Z n , 3 Z n , 36
Z n , 37 ] ( 15 ) ZS = [ b 1 , 1 b 1 , 2 b 1 , m b 2 , 1 b 2 , m b
36 , 1 b 36 , 2 b 36 , m ] ( 16 ) ##EQU7##
[0334] As the equation (13) indicates, the amount of any aberration
can be defined by using the Zernike-variations table and the
wave-front aberration data (for example, terms' coefficients (e.g.
the second term's coefficient Z.sub.2 through the 37th term's
coefficient Z.sub.37) of the Zernike polynomial in which the
wave-front aberration is expanded). In other words, by specifying
desired aberration values in the form of f (equation (14)), and
solving the equation (13) with the known (created before)
Zernike-variations table, the values of terms' coefficients (e.g.
the second term's coefficient Z.sub.2 through the 37th term's
coefficient Z.sub.37) of the Zernike polynomial for each
measurement point within the field of the projection optical system
can be determined which values make the amount of a specific
aberration at a desired value.
[0335] That is, in the seventh method the specification of the
projection optical system is determined using as a standard the
wave-front aberration (terms' coefficients of the Zernike
polynomial in which the wave-front is expanded) for a space image
of the pattern where the amount of a specific aberration, e.g., a
line-width abnormal value (an index of coma) is at a given
value.
[0336] In any of the above methods of determining the
specification, the specification of the projection optical system
is determined based on information of the target that the exposure
apparatus must achieve, with using as a standard the information of
the wave-front on the pupil plane of the projection optical system,
that is, the overall information of light passing the pupil plane,
and therefore by making the projection optical system satisfying
the specification, the target of the exposure apparatus can be
securely achieved.
[0337] b. The Process of Making a Projection Optical System
[0338] Next, the process of making a projection optical system will
be described with reference to a flow chart in FIG. 11.
[Step 1]
[0339] First in a step 1, lens devices, lens holders for holding
the lens device, and a lens barrel for housing optical units each
comprising the lens device and the lens holder are made according
to given lens data in design which are optical members composing
the projection optical system. That is, a known lens-processing
apparatus processes given optical material to the lens devices such
that these have a radius of curvature and a thickness along the
axis, which were planned in design. And a known metal-processing
apparatus processes given material (stainless, brass, ceramic,
etc.) to the lens barrel for housing the optical units comprising
the lens device and the lens holder such that it has dimensions
which were planned in design.
[Step 2]
[0340] In a step 2, the surface shapes of the lens devices of the
projection optical system PL made in the step 1 are measured by,
for example, a Fizeau-type interferometer which employs a He--Ne
gas laser emitting light having a wavelength of 633 nm, an Ar laser
emitting light having a wavelength of 363 nm, or a light source
which converts an Ar-laser light into a higher-harmonic wave having
a wavelength of 248 nm from an Ar laser. The Fizeau-type
interferometer measures by a pick-up unit such as CCD an
interference fringe caused by light reflected by a reference
surface on the surface of a condenser lens on the optical path and
light reflected by the surface of a lens device to be measured, so
that it can accurately obtain the shape of the surface to be
measured. Obtaining the shape of the surface (lens surface) of an
optical device such as a lens by using the Fizeau-type
interferometer is disclosed in, for example, Japanese Patent
Laid-Open No. 62-126305 and Japanese Patent Laid-Open No. 6-185997,
and thus its detailed description is omitted.
[0341] For the lens surfaces of all lens devices forming part of
the projection optical system PL, the measuring of the shape of the
surface of an optical device using the Fizeau-type interferometer
is performed, and the measurement results are stored in a memory
such as RAM or a storage unit such as a hard disk of the second
communication server 130 through an input unit (not shown) such as
a console.
[Step 3]
[0342] After the completion of, in step 2, measuring the shapes of
the lens surfaces of all lens devices forming part of the
projection optical system PL, the plurality of optical units each
comprising the lens device and a lens holder for holding the lens
device which are processed according to design values are assembled
individually. A plurality of, for example, four units of these
optical units each have the movable lens 13.sub.1 through 13.sub.4
and a double-structured lens holder described above which has an
inner lens holder for holding the movable lens 13.sub.1 through
13.sub.4 and an outer lens holder for holding the inner lens
holder, between which the positional relation are adjustable
through a mechanical adjustment mechanism. The double-structured
lens holder further comprises the above driving devices arranged in
respective, predetermined positions.
[0343] Then the plurality of optical units are assembled
individually by sequentially dropping these and a spacer each time
between these into the lens barrel through its upper opening. The
optical unit which was first dropped in the lens barrel is
supported by a protrusion in the lower end of the lens barrel via a
spacer, and when all the optical units have been accommodated in
the lens barrel, the assembly ends. During the assembly, distances
between the optical surfaces (lens surfaces) of the lens devices
are measured by a tool (micrometer, etc.) with taking into account
the thickness of the spacers to be accommodated in the lens barrel.
And the assembly and the measurement are repeated to obtain final
distances upon the completion of the assembly in the step 3 between
the optical surfaces (lens surfaces) of the lens devices in the
projection optical system PL.
[0344] Incidentally, during the making process including the
assembly, the movable lenses 13.sub.1 through 13.sub.4 are fixed in
their neutral positions. Although the explanation is omitted, the
pupil aperture stop 15 is instaled in the projection optical system
PL in the assembly.
[0345] The results of measuring, during the assembly and upon its
completion, distances between the optical surfaces (lens surfaces)
of the lens devices in the projection optical system PL are stored
in a memory such as RAM or a storage unit such as a hard disk of
the second communication server 130 through the input unit (not
shown) such as a console. It is remarked that in the assembly the
optical units may be adjusted as needed.
[0346] At that time, relative distances along the optical axis
between the optical devices are changed via, e.g., a mechanical
adjustment mechanism, or the optical devices are tilted to a
direction perpendicular to the optical axis. Moreover, the lens
barrel may have a tapped hole made therein and a screw which screws
through the tapped hole and which touches the lens holder so that
the lens holder can be displaced in a direction perpendicular to
the optical axis to adjust eccentricity, etc., thereof by screwing
the screw with a tool such as a screw-driver.
[Step 4]
[0347] Next, a step 4 measures the wave-front aberration due to the
projection optical system PL assembled in the step 3.
[0348] Specifically, the projection optical system PL is attached
to the body of a large-sized wave-front measuring apparatus (not
shown), and the wave-front aberration is measured. The principle of
the wave-front measuring apparatus measuring the wave-front is the
same as in the wave-front-aberration measuring unit 80 and thus its
detailed description is omitted.
[0349] As a result of measuring the wave-front, terms' coefficients
Z.sub.i (i=1, 2, through 81) of the Zernike polynomial (fringe
Zernike polynomial) in which the wave-front in the projection
optical system is expanded are obtained. Thus when the second
communication server 130 is connected with the wave-front measuring
apparatus, the terms' coefficients Z.sub.i of the Zernike
polynomial are automatically stored in a memory such as RAM (or a
storage unit such as a hard disk) of the second communication
server 130. While in the above description the wave-front measuring
apparatus outputs the coefficients up to the 81st term of the
Zernike polynomial in order to calculate higher-order components of
the aberrations due to the projection optical system PL,
coefficients up to the 37th term as in the wave-front-aberration
measuring unit or coefficients over the 81st term may be
output.
[Step 5]
[0350] In a step 5, the projection optical system PL is adjusted
based on the wave-front aberration measured in the step 4 such that
the wave-front aberration satisfies the specification determined
according to one of the first through seventh methods of
determining the specification.
[0351] Before the adjustment of the projection optical system PL,
the second communication server 130 reproduces optical data in the
making process of the projection optical system PL based on
information in the memory, that is, the shape information of the
surfaces of the optical devices obtained in the step 2, the
information of distances between the optical surfaces of the lens
devices obtained in the assembly of the step 3 and optical basic
data stored beforehand, which reproduced data is used to calculate
adjustment amounts for the optical devices.
[0352] That is, a basic database for adjustment is already stored
in the hard disk of the second communication server 130, which
database contains, for all the lens devices of the projection
optical system PL, the variation of each term's coefficient Z.sub.i
of the Zernike polynomial relative to a unit drive amount in each
of the six directions where the lens devices are movable, which
variation is calculated based on design values of the projection
optical system, the database being a matrix given by expanding the
matrix O so as to contain non-movable lenses as well as the movable
lenses. The second communication server 130 performs a
predetermined computation based on the optical data in the making
process for the projection optical system PL to correct the basic
database for adjustment.
[0353] And when one of the first through sixth methods is selected,
the second communication server 130, using a predetermined
computing program and the least-squares method, calculates drive
amount for each lens device in each of the six directions where the
lens devices are movable, based on the corrected basic database,
the target values for the wave-front, i.e. limits for terms'
coefficients Z.sub.i of the Zernike polynomial given by the
selected method of determining the specification, and measured
values of the terms' coefficients Z.sub.i of the Zernike
polynomial, which are a result of measurement by the wave-front
measuring apparatus.
[0354] Then the second communication server 130 displays on screen
information of drive amounts (may be zero) for the lens devices in
each of the six directions where the lens devices are movable.
[0355] According to the display, an engineer (or operator) adjusts
the lens devices, so that the projection optical system PL is
adjusted so as to satisfy the specification determined according to
the selected method of determining the specification.
[0356] Specifically, when the first method is selected as the
method of determining the specification, the projection optical
system PL is adjusted such that the coefficients of specific terms
selected based on the target information out of the terms of the
Zernike polynomial in which the wave-front in the projection
optical system is expanded are not over the limits. When the second
method is selected, the projection optical system PL is adjusted
such that the RMS value of terms' coefficients of the Zernike
polynomial in which the wave-front within the field of the
projection optical system is expanded is not over the limit. When
the third method is selected, the projection optical system PL is
adjusted such that terms' coefficients of the Zernike polynomial in
which the wave-front in the projection optical system is expanded
are not over the respective limits. When the fourth method is
selected, the projection optical system PL is adjusted such that
the RMS value, within the field, of the coefficients of terms (n'th
order, m.theta. terms), which correspond to a given aberration, out
of the terms of the Zernike polynomial in which the wave-front
within the field of the projection optical system is expanded is
not over the limit. When the fifth method is selected, the
projection optical system PL is adjusted such that the RMS value,
within the field, of the coefficients of each group of m.theta.
terms having the same m.theta. value out of terms, which correspond
to a given aberration, out of the terms of the Zernike polynomial
in which the wave-front within the field of the projection optical
system is expanded is not over the limit. When the sixth method is
selected, the projection optical system PL is adjusted such that
the RMS value, within the field, of coefficients given by weighting
according to the target information the coefficients of the terms
of the Zernike polynomial in which the wave-front within the field
of the projection optical system is expanded is not over the
limit.
[0357] When the seventh method is selected, the second
communication server 130 performs a simulation for obtaining a
space image formed on the image plane when the pattern is projected
by the projection optical system PL based on the pattern
information contained in the target information, and analyzes the
simulation result to adjust the projection optical system PL such
that the projection optical system satisfies the wave-front
aberration amount allowed for transferring the pattern finely. In
the simulation, based on linear combinations between sensitivities
(Zernike Sensitivity) of the coefficients of the terms of the
Zernike polynomial, in which the wave-front in the projection
optical system is expanded, to a watched aberration (or an index)
for the pattern (object pattern) and the coefficients of the terms
of the Zernike polynomial, the second communication server 130
obtains the space image, which sensitivities are given by
Zernike-variations tables which were created beforehand in the same
way as above, and calculates a drive amount for each lens device,
which makes the amount of the watched aberration at or below a
limit, based on the space image and by using the least-squares
method.
[0358] Then the second communication server 130 displays on screen
information of drive amounts (may be zero) for the lens devices in
each of the six directions where the lens devices are movable.
According to the display, an engineer (or operator) adjusts the
lens devices, so that the projection optical system PL is adjusted
so as to satisfy the specification determined according to the
seventh method of determining the specification.
[0359] In any of the methods, because the projection optical system
PL is adjusted based on a result of measuring the wave-front in the
projection optical system, higher-order components of the
wave-front aberration can be adjusted simultaneously as well as
lower-order components, without considering the order of
aberrations to be adjusted as in the prior art. Therefore, it is
possible to adjust the optical characteristic of the projection
optical system very accurately and easily, and the projection
optical system PL can be made which substantially satisfies the
determined specification.
[0360] Although, in this embodiment, after, in step 4, measuring
the wave-front aberration and installing the not-adjusted
projection optical system in the exposure apparatus, the projection
optical system is adjusted, the projection optical system adjusted
may be installed in the exposure apparatus after having adjusted
the projection optical system (reprocessing, replacement, etc., of
optical devices). Here, for example, an operator may adjust the
projection optical system by adjusting the positions of optical
devices without using the imaging-characteristic adjusting
mechanism. Further, based on the result of, after installing the
projection optical system in the exposure apparatus, measuring the
wave-front aberration with the wave-front-aberration measuring unit
80 or the measurement reticle R.sub.T again, the projection optical
system is preferably readjusted.
[0361] While in the above measuring of the wave-front upon the
adjustment of the projection optical system, the wave-front
measuring unit uses a space image formed through a pinhole and the
projection optical system PL, not being limited to this, it may use
the pattern formed on a wafer W by projecting, for example, the
image of a predetermined measurement pattern of the measurement
reticle R.sub.T through a pinhole and the projection optical system
PL.
[0362] It is remarked that in order to make easy reprocessing of
optical devices of the projection optical system PL, after
identifying an optical device that needs reprocessing based on a
result of the wave-front measuring apparatus measuring the
wave-front aberration, reprocessing the optical device and
readjusting other optical devices may be performed at the same
time. Furthermore, if reprocessing or replacement of optical
devices of the projection optical system is necessary, the
reprocessing or replacement is preferably performed before
installing the projection optical system in the exposure
apparatus.
[0363] Next, the method of making the exposure apparatus 122 will
be described.
[0364] First in the making of the exposure apparatus 122, the
illumination optical system 12 comprising a plurality of lens
devices and mirrors is assembled as a unit while the projection
optical system PL is assembled as a unit in the above way. And a
reticle stage system and a wafer stage system, which each comprise
a lot of mechanical elements, are assembled as individual units,
and optical adjustment, mechanical adjustment, electric adjustment,
etc., are performed so that these achieve desirable performance.
During the adjustments, the projection optical system PL is also
adjusted in the above way.
[0365] Next, the illumination optical system 12 and the projection
optical system PL are installed in an exposure-apparatus main body,
and the reticle stage system and the wafer stage system are
attached to the exposure-apparatus main body, and these are
connected together with electric wires and pipes.
[0366] Then, optical adjustment is performed on the illumination
optical system 12 and the projection optical system PL because,
between before and after being installed in the exposure-apparatus
main body, optical characteristics, particularly the imaging
characteristic of the projection optical system PL, are different.
In this embodiment, upon the optical adjustment of the projection
optical system PL after being installed in the exposure-apparatus
main body, the wave-front aberration is measured in the same way as
above after having attached the wave-front-aberration measuring
unit 80 to the Z-tilt stage 58. Wave-front information of
measurement points as a result of measuring the wave-front
aberration is sent via the network from the main controller 50 of
the exposure apparatus to the second communication server 130,
which, using, e.g., the least-squares method, calculates and
displays drive amounts for the lens devices in each of the six
directions where the lens devices are movable, in the same way as
in adjustment in the making of the projection optical system PL as
a single unit.
[0367] And according to the display, an engineer (or operator)
adjusts the lens devices, so that the projection optical system PL
is made which securely satisfies the specification determined.
[0368] Although it is possible for the main controller 50 to
automatically perform the final adjustment on the projection
optical system PL via the imaging-characteristic correcting
controller 48 according to instructions from the second
communication server 130 in the making process, the movable lenses
are preferably kept in their neutral positions after the completion
of making the exposure apparatus in order to ensure enough drive
stroke of driving devices just after having introduced into a
semiconductor-manufacturing factory. Furthermore, because
higher-order components of the wave-front aberration are supposedly
difficult to automatically correct, the positions, etc., of the
lenses, etc., are preferably readjusted.
[0369] It is remarked that for example when the above readjustment
does not yield a desirable performance, some lenses need to be
reprocessed or replaced. In order to make easy reprocessing of
optical devices of the projection optical system PL, an optical
device that needs reprocessing may be, as described above,
identified based on a result of a wave-front measuring apparatus
measuring the wave-front aberration in the projection optical
system PL before installing the projection optical system PL in the
exposure-apparatus main body, or reprocessing the optical device
and readjusting other optical devices may be performed at the same
time.
[0370] Moreover, optical devices of the projection optical system
PL may be individually replaced or, when the projection optical
system has a plurality of lens barrels, lens barrels as units may
be replaced. Furthermore, in reprocessing the optical device, its
surface may be processed so as to become non-spherical, if
necessary. Yet further, in adjusting the projection optical system
PL only the position (or distance from another), tilt, etc., of an
optical device thereof may be changed, or, when the optical device
is a lens, its eccentricity may be changed, or it may be rotated
about the optical axis AX.
[0371] After that, overall adjustment (electrical adjustment,
operation verification, etc.) is performed. By this, the exposure
apparatus 122 of this embodiment has been made which can accurately
transfer a pattern on a reticle R onto a wafer W by the projection
optical system PL whose optical characteristic has been adjusted
very accurately. It is remarked that the making of the exposure
apparatus is preferably performed in a clean room where the
temperature and cleanliness are controlled.
[0372] As described above, according to the computer system 10 of
this embodiment and the methods of determining the specification of
the projection optical system, the specification of the projection
optical system is determined based on target information that the
exposure apparatus 122 should achieve and a given standard of the
wave-front aberration due to the projection optical system PL. That
is, the specification of the projection optical system is
determined using a given standard of information of the wave-front
on the pupil plane of the projection optical system. Therefore, the
projection optical system PL is adjusted based on a result of
measuring the wave-front aberration, for example, in making the
projection optical system PL according to the determined
specification, so that higher-order components of the wave-front
aberration are simultaneously adjusted as well as lower-order
components. Thus compared with the prior art where after the
adjustment of the projection optical system for correcting
lower-order components, the adjustment of the projection optical
system for correcting higher-order components is performed based on
a result of detecting the higher-order components by tracing
light-rays, the process of making the projection optical system is
obviously simple. In addition, because the specification is
determined based on the target information, the exposure apparatus
122 comprising the projection optical system can securely achieve
the target.
[0373] In addition, in this embodiment, in adjusting the projection
optical system in the process of making the projection optical
system and exposure apparatus, after determining the specification
and measuring the wave-front aberration due to the projection
optical system PL, the projection optical system PL is adjusted
based on the measurement result so as to satisfy the specification.
Therefore, the projection optical system PL can be easily and
securely made which satisfies the specification. Thus, sequentially
performing the adjustments for lower-order components and for
higher-order components and tracing light-rays for the adjustment
as in the prior art are not needed, so that the process of making
the projection optical system PL becomes simpler and that the
exposure apparatus 122 comprising the projection optical system
securely achieves the target.
[0374] In this embodiment, both before and after installing the
projection optical system PL in the exposure-apparatus main body,
the wave-front aberration is measured. In the former, the
wave-front aberration measuring apparatus very accurately measures
the wave-front in the projection optical system, and in the latter
the optical characteristic of the projection optical system can be
very accurately adjusted regardless of whether or not environmental
conditions are different between before and after installing the
projection optical system PL in the exposure-apparatus main body.
Alternatively, either before or after installing the projection
optical system PL in the exposure-apparatus main body, the
wave-front aberration may be measured.
[0375] In any of the cases, because the projection optical system
PL is adjusted based on a result of measuring the wave-front in the
projection optical system, higher-order components of the
wave-front aberration can be adjusted simultaneously as well as
lower-order components, without considering the order of
aberrations to be adjusted as in the prior art. Therefore, it is
possible to adjust the optical characteristic of the projection
optical system very accurately and easily, and the projection
optical system PL can be made which substantially satisfies the
determined specification.
[0376] According to the exposure apparatus 122 of this embodiment,
the main controller 50 measures the wave-front in the projection
optical system via the wave-front-aberration measuring unit 80 (or
the measurement reticle R.sub.T) as described above, and controls
the imaging-characteristic adjusting mechanism (48, 13.sub.1
through 13.sub.4), etc., using the result of measuring the
wave-front, which provides overall information on light passing
through the pupil plane of the projection optical system.
Therefore, the imaging characteristic of the projection optical
system PL is automatically adjusted using the result of measuring
the wave-front, so that the image of a pattern formed by the
projection optical system PL is adjusted to be fine.
[0377] In addition, because the exposure apparatus 122 of this
embodiment comprises the projection optical system PL that has been
made according to the making method and adjusted in terms of
higher-order components of the wave-front aberration as well as
lower-order components in the later adjustment as well as in the
making process, a pattern of a reticle R can be accurately
transferred onto a wafer W by the projection optical system PL.
[0378] In addition, according to the computer system 10 of this
embodiment, the wave-front-aberration measuring unit 80 of the
exposure apparatus 122 measures the wave-front in the projection
optical system PL. The first communication server 120 sends the
result of the wave-front-aberration measuring unit 80 measuring the
wave-front in the projection optical system PL to the second
communication server 130, which controls the imaging-characteristic
adjusting mechanism (48, 13.sub.1 through 13.sub.4), using the
result of measuring the wave-front. Therefore, the imaging
characteristic of the projection optical system PL is accurately
adjusted using information of the wave-front on the pupil plane of
the projection optical system, that is, overall information on
light passing through the pupil plane, so that the image of a
pattern formed by the projection optical system PL is adjusted to
be optimal. The second communication server 130 can be disposed in
a remote position from the exposure apparatus 122 and the first
communication server 120 connected thereto, in which case the
imaging characteristic of the projection optical system PL and thus
the image of a pattern formed by the projection optical system PL
can be very accurately adjusted in remote control.
[0379] According to the computer system 10 of this embodiment and
the method of determining optimum conditions, when a host computer
managing the exposure apparatus 122 or an operator has inputted
information on exposure conditions including pattern information
into the first communication server 120, the second communication
server 130 repeats the simulation for obtaining a space image of
the pattern formed on the image plane based on the pattern
information included in the information on exposure conditions
received from the first communication server 120 through the
network and known aberration information of the projection optical
system PL, and determines optimum exposure conditions by analyzing
the simulation results. Therefore, the exposure conditions are
almost automatically set to be optimal.
[0380] According to the computer system 10 of this embodiment, when
adjusting the projection optical system PL upon, e.g., the
maintenance of the exposure apparatus 122, a service engineer,
etc., attaches the wave-front-aberration measuring unit 80 to the
Z-tilt stage 58 and instructs to measure the wave-front via the
input unit 45, so that the second communication server 130 very
accurately adjusts the imaging characteristic of the projection
optical system PL in remote control. Alternatively, a service
engineer, etc., using the measurement reticle R.sub.T, may measure
the wave-front aberration due to the projection optical system PL
of the exposure apparatus 122 in the above procedure, and input
position deviation data obtained by the measurement into the main
controller 50 of the exposure apparatus 122, in which case also the
second communication server 130 can very accurately adjust the
imaging characteristic of the projection optical system PL in
remote control.
[0381] Furthermore, the exposure apparatus 122 whose exposure
conditions are set to be optimal before exposure can, with high
overlay accuracy, transfer a fine pattern on a reticle R onto a
wafer W via the projection optical system PL whose imaging
characteristic has been adjusted accurately.
[0382] Although the above embodiment describes the case where an
adjusting apparatus for adjusting the image of a pattern formed by
the projection optical system PL is constituted by the
imaging-characteristic adjusting mechanism for adjusting the
imaging characteristic of the projection optical system PL, this
invention is not limited to this. The adjusting apparatus may
alternatively or additionally include, for example, a mechanism
which drives at least one of the reticle R and the wafer W in the
direction parallel to the optical-axis AX or a mechanism which
shifts the wavelength of the illumination light EL. For example
when using the mechanism which shifts the wavelength of the
illumination light EL together with the imaging-characteristic
adjusting mechanism, the adjustment of the imaging characteristic,
as in the case of the movable lenses, is possible by using the
variation of the imaging characteristic in each of a plurality of
measurement points within the field of the projection optical
system PL, specifically wave-front data, for example the variations
of the second term's coefficient through the 37th term's
coefficient of the Zernike polynomial relative to a unit shift
amount of the illumination light EL, which were obtained by the
above simulation, etc., and contained in the database beforehand.
That is, performing the least-squares computation according to the
above second program with using the database gives an optimum shift
amount for the wavelength of the illumination light EL in terms of
obtaining an optimum image of a pattern formed by the projection
optical system, and based on the computing result, the wavelength
can be automatically adjusted.
[0383] Although the above embodiment describes the case of using
the exposure apparatus as an optical apparatus, not being limited
to this, the optical apparatus only has to comprise a projection
optical system.
[0384] Although the above embodiment describes the computer system
where the first communication server 120 as the first computer and
the second communication server 130 as the second computer are
connected with each other via a communication path including the
public telephone line, this invention is not limited to this. For
example, it may be a computer system where the first communication
server 120 and the second communication server 130 are connected
with each other via a communication path LAN 126' as shown in FIG.
12, such as an in-house LAN system installed in the
research-and-development section of an exposure-apparatus
maker.
[0385] In the construction of such an in-house LAN system, the
first communication server 120 is installed on a clean room side in
the research-and-development section such as a place where an
exposure apparatus is assembled and adjusted (hereinafter, called a
"site"), and the second communication server 130 is installed in an
office remote from the site. And an engineer in the site sends
measurement data of the wave-front aberration and information of
exposure conditions (including pattern information) for an exposure
apparatus under experiment to the second communication server 130
on the office side via the first communication server 120. And an
engineer on the office side instructs the second communication
server 130 to perform automatic correction of the imaging
characteristic of the projection optical system PL of the exposure
apparatus 122 based on the received information, in which server
130 a program being developed by them is already installed, and
receives the result of measuring the wave-front aberration due to
the projection optical system PL after the adjustment of the
imaging characteristic to confirm the effect of the adjustment of
the imaging characteristic. The result can also be used in
developing the program.
[0386] Alternatively, an engineer in the site may send pattern
information from the first communication server 120 to the second
communication server 130 and make it determine an optimum
specification of the projection optical system for the pattern.
[0387] In addition, the first communication server 120 and the
second communication server 130 may be connected with each other by
radio.
[0388] Although the above embodiment and modified ones describe a
case where a plurality of exposure apparatuses 122.sub.1 through
122.sub.3 are arranged which are connected with each other via a
communication path, this invention is not limited to this, and
there may be only one exposure apparatus.
[0389] Although the above embodiment describes the case of
determining the specification of the projection optical system
using the computer system 10, the technical idea of determining the
specification of the projection optical system using a standard for
the wave-front can be used irrelevantly to the computer system 10.
That is, in a business between the makers A and B, the maker B may
determine, using a standard for the wave-front, the optimum
specification of the projection optical system for pattern
information, etc., provided by the maker A. Also this case has the
advantage, when making the projection optical system based on the
specification determined using a standard for the wave-front, that
the process thereof is simpler.
[0390] In addition, in the above embodiment, the second
communication server 130 calculates adjustment amounts ADJ1 through
ADJm of the movable lenses 13.sub.1 through 13.sub.4 using the
second program and based on the result of measuring the wave-front
aberration of the projection optical system of the exposure
apparatus 122, and sends the adjustment-amounts data to the main
controller 50 of the exposure apparatus 122, which gives the
imaging-characteristic correcting controller 48 instruction-values
according to the adjustment-amounts ADJ1 through ADJm to move in
the movement directions the movable lenses 13.sub.1 through
13.sub.4 by, so that the adjustment of the imaging characteristic
of the projection optical system PL is performed in remote control.
However, not being limited to this, the exposure apparatus 122 may
be constructed to automatically adjust the imaging characteristic
of the projection optical system based on the result of measuring
the wave-front aberration and using the same program as the second
program.
[0391] Note that in the manufacturing of microprocessors for
example, when forming gates, a phase-shift reticle as a phase-shift
mask, particularly, a phase-shift reticle of a
space-frequency-modulation-type (Levenson type) is used together
with small a illumination. Specifically, under an illumination
condition that a coherence factor (a value) is smaller than 0.5,
preferably below about 0.45, the phase-shift reticle is
illuminated. Here, the best focus position within the exposure area
in the field of the projection optical system deviates due to the
aberrations of the projection optical system (e.g. astigmatism,
spherical aberration, etc.), so that the depth of focus is smaller,
which exposure area is conjugate to the illumination area with
respect to the projection optical system and is a projection area
on which the image of the pattern on a reticle is formed by
exposure illumination light.
[0392] Therefore, in the making of the projection optical system,
by, e.g., adjusting the aberrations of the projection optical
system (e.g. field curvature, astigmatism, spherical aberration,
etc.) based on the deviation of the best focus position (image
surface) within the exposure area of the projection optical system
due to the use of the phase-shift reticle, the best focus position
within the exposure area is preferably displaced partially and
deliberately. In this case, focus-correction for correcting the
aberrations may be performed so as to make a so-called overall
focus difference small. By this, the deviation of the best focus
position upon using the phase-shift reticle is greatly reduced, so
that the pattern of the phase-shift reticle is transferred onto a
wafer with a larger depth of focus than before.
[0393] Furthermore, the same problem may occur when a phase-shift
reticle is used in an exposure apparatus in a device-manufacturing
factory. Therefore, the best focus position within the exposure
area is preferably displaced partially and deliberately by
adjusting the aberrations with using a mechanism for adjusting the
imaging characteristic of the projection optical system such as a
mechanism that drives at least one optical device of the projection
optical system via an actuator (piezo device, etc.). Here, at least
one of the field curvature and astigmatism or additionally the
spherical aberration in the projection optical system is adjusted.
Also in this case, focus-correction for correcting the aberrations
may be performed so as to make the overall focus difference
small.
[0394] Before the adjustment the imaging characteristic of the
projection optical system, the imaging characteristic thereof,
mainly, the image-surface (representing the best focus positions in
the exposure area) may be obtained by computing from design data of
the projection optical system or by actually measuring the imaging
characteristic.
[0395] In the former case, a method of computing by using
Zernike-variations tables described above may be used. In the
latter case, the imaging characteristic may be obtained from the
wave-front aberration measured, or from the result of detecting the
pattern image of the reticle by a space-image measuring unit having
a light-receiving surface on the wafer stage or from the result of
detecting an image of the reticle's pattern (latent image or resist
image) projected onto a wafer.
[0396] Here, it is preferable that with using a pattern image
formed under almost the same exposure conditions, e.g. small
.sigma. illumination, as in manufacturing devices, the imaging
characteristic of the projection optical system is obtained.
[0397] In addition, the imaging characteristic of the projection
optical system in which the deviation of the best focus position
upon using the phase-shift reticle is reduced is measured again
after the assembly or adjustment.
[0398] At this point of time, the deviation of line width in the
best focus position surface may occur due to residual aberration in
the projection optical system. If the deviation is above a limit,
at least part of the projection optical system needs to be replaced
or readjusted to make the aberration in the projection optical
system smaller.
[0399] Here, optical devices of the projection optical system may
be individually replaced or, when the projection optical system has
a plurality of lens barrels, lens barrels as units may be replaced.
Furthermore, at least one optical device may be reprocessed, and
especially when the optical device is a lens, its surface may be
processed so as to become non-spherical, if necessary. The optical
device is a refracting optical device such as a lens or a
reflecting optical device such as a concave mirror or an
aberration-correcting plate for correcting the aberrations
(distortion, spherical aberration, etc.), especially,
non-rotation-symmetry components due to the projection optical
system. Further, in adjusting the projection optical system only
the position (or distance from another), tilt, etc., of an optical
device thereof may be changed or, when the optical device is a
lens, its eccentricity may be changed or it may be rotated about
the optical axis AX. Such adjustment (replacement, reprocess, etc.)
may also be performed in the above embodiment.
[0400] Although the above embodiment describes the case where the
measurement reticle R.sub.T has a reference pattern as well as a
measurement pattern, the reference pattern is not necessarily
provided on an optical-characteristic measurement mask (in the
above embodiment, the measurement reticle R.sub.T). That is, the
reference pattern may be provided on another mask or on the
substrate (wafer) side and not on the mask side. That is, a
reference wafer is prepared by, after coating with a resist a wafer
where the image of the reference pattern is formed reduced to the
projection magnification times its original size, transferring the
measurement pattern onto the resist layer and then developing it,
and by measuring the position deviation of the measurement
pattern's resist image from the reference pattern on the reference
wafer, substantially the same measurement as in the above
embodiment is possible.
[0401] Although in the above embodiment the wave-front aberration
due to the projection optical system is calculated based on the
result of measuring the resist images which are obtained by, after
transferring the measurement and reference patterns on the wafer W,
developing it, not being limited to this, the result of measuring
the image (space image) of the measurement pattern projected onto a
wafer using the space-image measuring unit or of measuring the
latent images of the measurement and reference patterns formed in
the resist layer or images formed by etching a wafer may be used.
Also in this case, the wave-front aberration can be obtained in the
same procedure as in the above embodiment based on the result of
measuring the position deviation of the measurement pattern from a
reference position (e.g. projection position of the measurement
pattern planned in design). Instead of transferring the measurement
pattern onto the wafer, after transferring the reference pattern
onto the resist layer on a reference wafer on which the measurement
pattern is already formed, the position deviation of the
measurement pattern from the reference pattern may be measured by,
e.g., using a space-image measuring unit having a plurality of
apertures corresponding to the measurement pattern. Moreover,
although in the above embodiment the overlay-measuring unit
measures the position deviation, the alignment sensor may be used
which is provided in the exposure apparatus.
[0402] While in the above embodiment the coefficients up to the
37th term of the Zernike polynomial are used, the coefficients over
the 37th term, e.g. up to the 81st term, of the Zernike polynomial
may be used to calculate higher-order components of the aberrations
due to the projection optical system PL. That is, this invention is
irrelevant to the number of terms, and term numbers, of the Zernike
polynomial in use. In addition, depending on the illumination
condition the aberration in the projection optical system PL may be
caused deliberately, and thus in the above embodiment the optical
devices of the projection optical system PL may be adjusted for the
aim aberration to take on a given value and not zero or
minimum.
[0403] In the above embodiment the first communication server 120
inquires information of reticle to be used this time in, for
example, the exposure apparatus 122.sub.1 from the host computer
(not shown) managing the exposure apparatuses 122.sub.1 through
122.sub.3 and, based on the reticle information, searches a given
database to obtain the pattern information, or alternatively an
operator inputs the pattern information into the first
communication server 120 via an input unit. However, not being
limited to this, the exposure apparatus may further comprise a
reader BR such as a bar-code reader indicated by an imaginary line
in FIG. 2, by which the first communication server 120 reads a
bar-code, two-dimensional code, etc., attached to a reticle R being
transferred to the reticle stage RST, via the main controller 50 in
order to obtain the pattern information.
[0404] In addition, in the case of measuring the wave-front
aberration using the measurement reticle for example, the alignment
system ALG may detect the position deviation of the latent image of
the measurement pattern from that of the reference pattern, the two
latent images being formed in the resist layer on the wafer.
Moreover, in the case of measuring the wave-front aberration using
a wave-front-aberration measuring unit for example, the
wave-front-aberration measuring unit may be one having such a shape
that it can replace the wafer holder. In this case, the
wave-front-aberration measuring unit can be automatically
transported by a transport system (including a wafer loader) for
replacing a wafer or wafer holder. By implementing the above
various means, the computer system 10 can automatically adjust the
imaging characteristic of the projection optical system PL and set
best exposure conditions without the help of an operator or service
engineer. Although this embodiment describes the case where the
wave-front-aberration measuring unit 80 is attachable to and
detachable from the wafer stage, the wave-front-aberration
measuring unit 80 may be fixed on the wafer stage, in which case a
part of the wave-front-aberration measuring unit 80 may be provided
on the wafer stage while the rest is disposed separately from the
wafer stage. Although in this embodiment, wave-front aberration due
to the light-receiving optical system of the wave-front-aberration
measuring unit 80 is neglected, the wave-front aberration in the
projection optical system may be determined in view of the
wave-front aberration due to the light-receiving optical
system.
[0405] In addition, the exposure apparatus 122 alone may
automatically adjust the imaging characteristic of the projection
optical system PL and set best exposure conditions by using the
first through third programs and databases associated therewith,
described in the above embodiment and which are stored in an
information storage media or the storage unit 42 of the drive unit
46 thereof. Furthermore, the first through third programs may be
stored in an exclusive server (equivalent to the second
communication server 130) that is disposed in the factory of the
maker A and connected to the exposure apparatuses through LAN. The
point is that this invention is not limited to the construction in
FIG. 1, and that it does not matter where a computer (server, etc.)
storing the first through third programs is disposed.
[0406] Although the above embodiment describes the case where the
exposure apparatus is a stepper, not being limited to this, it may
be a scan-type exposure apparatus that is disclosed in, for
example, U.S. Pat. No. 5,473,410 and that transfers the pattern of
a mask while moving synchronously the mask and a substrate.
[0407] This invention can be applied not only to an exposure
apparatus for manufacturing semiconductor devices but also to an
exposure apparatus for transferring a liquid crystal display device
pattern onto a rectangular glass plate and an exposure apparatus
for producing membrane-magnetic heads, micro machines, DNA chips,
etc. Furthermore, this invention can be applied to an exposure
apparatus for transferring a circuit pattern onto glass plates or
silicon wafers to produce masks or reticles used by a light
exposure apparatus, an EUV exposure apparatus, an X-ray exposure
apparatus, a charged-particle-beam exposure apparatus employing an
electron or ion beam, etc.
[0408] In addition, the light source may be an ultraviolet pulse
illuminant such as an F.sub.2 laser, ArF excimer laser or KrF
excimer laser or a continuous illuminant such as an ultra-high
pressure mercury lamp emitting an emission line such as g-line (a
wavelength of 436 nm) or i-line (a wavelength of 365 nm).
[0409] Moreover, a higher harmonic wave may be used which is
obtained with wavelength conversion into ultraviolet by using
non-linear optical crystal after having amplified a single
wavelength laser light, infrared or visible, emitted from a DFB
semiconductor laser device or a fiber laser by a fiber amplifier
having, for example, erbium (or erbium and ytterbium) doped.
Furthermore, the projection optical system is not limited in
magnification to a reduction system and may be an even-ratio or
magnifying system. Yet further, the projection optical system is
not limited to a refracting system and may be a catadioptric system
having reflecting optical elements and refracting optical elements
or a reflecting system having only reflecting optical elements. It
is remarked that, when the catadioptric system or the reflecting
system is used as the projection optical system, the imaging
characteristic of the projection optical system is adjusted by
changing the positions, etc., of the reflecting optical elements
(concave mirror, reflective mirror, etc.) as the above-mentioned
movable optical devices. When F.sub.2 laser light, Ar.sub.2 laser
light, EUV light, or the like is employed as the illumination light
EL, the projection optical system PL may be a reflecting system
having only reflecting optical elements, and when Ar.sub.2 laser
light, EUV light, or the like is employed, a reticle R needs to be
of a reflective type.
[0410] It is remarked that the process of manufacturing
semiconductor devices comprises the steps of designing
function/performance of the devices; making reticles according to
the function/performance planned in the designing step; making
wafers from silicon material; transferring the pattern of the
reticle onto the wafer by using the above-mentioned exposure
apparatus; assembling the devices (including the steps of dicing,
bonding, and packaging); and inspection. According to this device
manufacturing method, because, in a lithography step, the exposure
apparatus of the above-mentioned embodiment performs exposure, the
pattern of a reticle R is transferred onto a wafer W through the
projection optical system PL whose imaging characteristic is very
accurately adjusted according to the pattern to be transferred or
based on the result of measuring the wave-front aberration, and
therefore it is possible to transfer the fine pattern onto the
wafer W with high overlay accuracy, so that the yield of the
devices as final products and the productivity are improved.
[0411] Although the embodiments according to the present invention
are preferred embodiments, those skilled in the art of lithography
systems can readily think of numerous additions, modifications and
substitutions to the above embodiments, without departing from the
scope and spirit of this invention. It is contemplated that any
such additions, modifications and substitutions will fall within
the scope of the present invention, which is defined by the claims
appended hereto.
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